The Endocrinology of Prostate Cancer

Mary Ellen Taplin and Shuk-Mei Ho

Department of Medicine, Division of Oncology (M.E.T.), and Department of Surgery, Division of Urology (S.-M.H.), University of Massachusetts School of Medicine, Worcester, Massachusetts 01655

Address all correspondence and requests for reprints to: Dr. Shuk-Mei Ho, Room 4-746A, Division of Urology, Department of Surgery, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, Massachusetts 01655. E-mail: Shuk-mei.Ho{at}umassmed.edu

Prostate cancer (PC) is the leading cancer diagnosis in men in the United States and is second only to lung cancer in male cancer-related death (1). In 2000 there were approximately 190,000 new cases of PC and 32,000 PC deaths. Not long ago, PC was considered an incidental problem of elderly men and as such was given relatively little research attention. In the last 15 yr there has been an amplification of interest in all aspects of PC biology and treatment. This shift stems from an aging population with an improved overall life expectancy. Basic research has been spurred by the development of sophisticated molecular biology techniques coincident with the development of prostate-specific antigen (PSA) serum testing that facilitates earlier detection and assessment of response to therapeutics.

This review focuses on recent advances in our knowledge of the endocrinology of PC and the application of hormone-based therapies. PC is an endocrine-responsive tumor. Huggins and Hodges (2) demonstrated the therapeutic effect of castration in the 1940s, and this approach remains the mainstay of systemic treatment today. Normal and aberrant prostate cellular function is governed chiefly by androgens. However, other nonandrogenic hormones, whose influence on the prostate can be synergistic or antagonistic, may also contribute to the etiology and progression of PC. A major challenge for PC management is the progression of the disease to androgen independence (AI)1 and hormone refractory state. This review addresses the role of steroid hormones in the development and progression of PC.

Synthesis, transport, and metabolism of sex hormones (Fig. 1)

Androgens are required for normal growth and functional activities of the human prostate. In men, the major circulating androgen is testosterone (T), with the testes producing over more than 95% and the adrenal gland less than 5% of the sex steroid (3). In both tissues, the {delta}-5 synthetic pathway, which results in androstenedione and T production, is the predominant pathway, whereas the {delta}-4 pathway leading to the synthesis of dehydroepiandrosterone (DHEA) and androstenediol is the minor pathway (3). Once synthesized, most of DHEA is inactivated via sulfation while a small fraction of this weak androgen is converted to androstenedione, then to T, in peripheral tissues and in the prostate (4). Testicular steroidogenesis in the Leydig cells is regulated primarily by the gonadotropin LH, whereas adrenal androgen production is under the control of ACTH. In healthy men, adrenal androgens contribute little to prostatic function, yet after orchiectomy or treatment with GnRH analogs this source of androgen may become significant in promoting PC growth (5).

T in circulation is bound to serum proteins, primarily sex hormone-binding globulin (SHBG), albumin and corticosteroid-binding globulin (6). It has been estimated that only 2–3% of T exists as the bioavailable free form (6). Among the three proteins, SHBG has the highest affinity for T and, therefore, plays an important role in regulating the amount of free T available to target tissues. In end organs such as the prostate, T is converted to the more potent intracellular androgen, 5{alpha}-dihydrotestosterone (DHT) by 5{alpha}-reductase activities. Two 5{alpha}-reductases have been reported. Type I 5{alpha}-reductase is present in most tissues of the body whereas Type II 5{alpha}-reductase, encoded by the SRD5A2 gene located on chromosome 2p23 (7), is the dominant isoenzyme in genital tissues, including the prostate (8). Recent studies have, however, reported expression of Type I 5{alpha}-reductase in prostatic epithelial cells (9). When finasteride, a specific Type II 5{alpha}-reductase inhibitor, was administered to men for treatment of benign prostatic hyperplasia (BPH) serum DHT was suppressed by 70% and prostate DHT by as much as 85–90% (8). The remaining DHT in the prostate likely results from the activity of Type I isoenzyme. Two large international multicenter, Phase III trials have documented the safety and efficacy of finasteride in the treatment BPH (8). However, the efficacy of finasteride in preventing PC development will have to await final reporting of data from the Prostate Cancer Prevention Trial, which has been scheduled to complete its primary end point in October 2004 (10).

Intracellular DHT is rapidly metabolized to 3{alpha}, 17ß-androstenediol (3{alpha}-diol), which can be back-converted to DHT, or to 3ß, 17ß-androstenediol (3ß-diol), which is instantly and irreversibly converted to the water soluble, inactive triol steroids. The key enzyme responsible for this inactivation pathway is the Type II 3ß-hydroxysteroid dehydrogenase encoded by the HSD3B2 located on chromosome 1p13 (7).

Lastly, it is well established that circulating androgens are also converted to estrogens extragonadally (75–90%) at various peripheral tissues mediated by the enzyme aromatase (coded by the CYP19 gene) (11). Interestingly, both aromatase protein and message have been identified in the human prostate, suggesting local aromatization could provide a source of estrogen to the prostate (12, 13). In fact, intraprostatic synthesis of estrogens has been implicated in the etiology of BPH in men (14, 15), but its significance in prostate carcinogenesis is currently uncertain.

Epidemilogic evidence implicating involvement of endogenous sex hormones in prostate carcinogenesis (Fig. 1Go)

Because the human prostate is an androgen-dependent organ it is logical to presume that prostate malignancy develops under abnormal androgenic stimulation. This notion is, to some extent, supported by observations that eunuchs do not develop PC (16) and that a higher incidence of PC is found in men who used androgens as anabolic agents or therapeutics (17, 18, 19). Additionally, exposure to maternal estrogen during fetal life leads to the development of squamous metaplasia in the fetal prostate (20), and animal model systems have implicated estrogens as cancer-causing agents in the rat prostate (21). Collectively, these findings raise the possibility that sex hormones contribute to prostatic carcinogenesis. In addition, because androgens undergo extensive metabolic activation and inactivation, both extra- and intraprostatically polymorphisms in genes encoding metabolic enzymes involved in these processes may influence PC risk.



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Figure 1. Biosynthesis, transport, activation, and inactivation of androgens.

 
After a careful and extensive review of data from all existing epidemiologic studies, Bosland (22) has recently concluded that population-based case-control studies have revealed no clear associations between PC risk and circulating sex hormones, with few exceptions. A fairly comprehensive list of hormonal parameters has been investigated including LH, FSH, total T, free T, androstenedione, DHEA, 3{alpha}, 17ß-androstenediol glucuronide, androsterone glucuronide, estrone, estradiol (E2), and SHBG. In most studies (23, 24, 25, 26, 27), an association was found between increased risk and increased ratio of T to DHT, suggesting a relationship between reduced 5{alpha}-reductase activity and PC risk. No associations were found between risk and the levels of androsterone glucuronide and 3{alpha}-diol glucuronide, indicators of 5{alpha}-reductase activity. These epidemiologic data agree with the general observation that PC seems to arise from the hormonal milieu of the aging human male, which is marked by steady declines in circulating androgens (28) and reduced production of DHT in the prostatic epithelium (29).

Another valuable epidemiologic data set that has shed light on the contribution of sex steroids to prostate carcinogenesis was derived from studies on susceptible populations (22). Overall, a weak but somewhat consistent association between higher circulating T and/or estrogens and high-risk ethnic/racial groups has been observed. For example, Ross et al. (30) found higher T, free T, and estrone in 50 healthy young African-American men (high risk) when compared with 50 young European-American males (low risk). In agreement, de Jong et al. (31) found 71% higher circulating total T levels in Caucasian-Dutch men (high risk) than in Japanese men (low risk). These data would suggest higher circulating levels of sex steroid as PC risk factors. However, in a follow-up study in 1992, Ross et al. (32) found serum T levels in Japanese men (low risk) were not lower than those of the United States whites and blacks (high-risk groups) (32). Similarly, Wu et al. (33) demonstrated higher serum T levels in Asian-Americans (low risk) than in European-American men (high risk). Although circulating sex hormone levels in adult males have not been established as definitive etiological factors for PC, fetal or adolescent exposure to high levels of sex hormones may have long-lasting impacts. Serum T levels were 47% higher in black women than in white women during pregnancy, and E2 levels were 37% higher (34). E2 levels were lower in young black boys than in white boys but higher in older black boys and young black men than in their age-matched white counterparts (35). The notion that sex hormones may have "imprinting" effects on PC susceptibility during adulthood is an intriguing question that warrants further investigation.

Lastly, several polymorphisms in genes associated with sex hormone activation/inactivation have been implicated in the etiology of PC. To date, studies have been focused on the following genes: 1) the SRD5A2 gene that encodes Type II 5{alpha}-reductase responsible for androgen activation (36, 37, 38); 2) the CYP17 gene that encodes 17{alpha}-hydroxylase and 17,20-lyase activity accountable for regulation of androgen (39) and estrogen (40) biosynthesis; and 3) the HSD3B2 gene that encodes 3ß-hydroxysteroid dehydrogenase responsible for DHT catabolism (41, 42). It has been shown that prevalence of high/low activity alleles in specific ethnic/racial groups could partially explain some of the observed difference in PC susceptibilities among these populations (22).

Androgen receptor (AR) and prostate carcinogenesis (Table 1Go)

The AR, a member of the superfamily of ligand-dependent nuclear transcription factors (43, 44), was first described in 1969 (45) and cloned in 1988 (46). The gene is located on the X-chromosome at Xq11–12, contains 8 exons, and spans a length of approximately 90 kb of DNA (47). Transcription occurs from one of two initiation sites (48, 49), producing two AR transcripts (10 kb and 7 kb long) with different 3' untranslated sequence lengths that are expressed in most target tissues (50). The primary amino acid (aa) sequence is approximately 910–919 in length, with a calculated molecular weight of 98 kDa (51). Similar to other steroid receptor proteins, the full-length AR protein contains four functional domains: the amino-terminus regulatory domain, a DNA-binding domain, a hinge region, and the ligand-binding domain (52).


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Table 1. Types of AR alterations that could contribute to the development of HRPC

 
The N terminus, encoded by exon 1 (A/B region), comprises almost half of the AR molecule and harbors one of two transcriptional activation function (TAF) sites (TAF-1, a.a 141–338) (53). It has several homopolymeric amino acid stretches, including a polyglutamine-, a polyglycine-, and a polyproline-repeat (54). Exons 2 and 3 encode the DNA-binding domain (C region), which contains two zinc fingers essential for androgen-response element recognition. At the end of the C region and within the hinge region (D region), encoded by the proximal region of exon 4, is a nuclear localization signal (aa 617–633) that directs the AR to the cell nucleus (55). The C-terminal ligand-binding domain (E/F region) is encoded by part of exon 4 and entire exons 5–8. The ligand-binding domain (253 aa) is highly hydrophobic and harbors the second TAF site (TAF-2, aa 360–528 (56). Unliganded ARs are bound to heat shock proteins (HSPs) 90, 70, and 56, which stabilize their tertiary structure and prevent them from constitutive activation (57). Androgen binding to ARs leads to dissociation from HSPs, dimerization, phosphorylation, interaction with androgen-response elements, recruitment of coregulators, formation of the preinitiation complex, and ultimately transcriptional activation of androgen-regulated genes (52).

Results from immunohistochemistry studies reveal that AR is present in primary site and metastatic PCs regardless of stage and grade, as well as in hormone refractory cancers (58, 59, 60, 61, 62). AR immunoreactivity is heterogeneous within and among cancer foci and bears no apparent correlation with disease prognosis or with duration of responsiveness to hormone therapy (59, 60, 62, 63, 64). However, some studies have noted that an increase in AR heterogeneity or decrease in AR positivity in PC is associated with higher grade and poorer prognosis (59, 60, 63, 64, 65). In contrast to epithelial (adenocarcinoma) cancers, prostate tumors composed primarily of small cells and neuroendocrine cells are devoid of AR (66, 67). Thus, it is possible that clonal propagation of AR-negative malignant cells may give rise to some androgen-independent prostatic carcinoma (66).

Similar to the roles it plays in the normal prostate, AR activation in androgen-responsive PC leads to a complexity of proliferative, apoptotic, and angiogenic events, which collectively control tumor growth (68). It has been shown that androgens enhance expression of cyclin-dependent kinase 2 and 4 and down-regulation of the cell cycle inhibitor p16 (69). Furthermore, AR activation in PC cells leads to up-regulation of p21(WAF1/CIP1), a presumed antiapoptotic factor (70). In this regard, expression of p21 is significantly increased in high Gleason score, fast proliferating, advanced PCs (71). AR seems to exert both positive and negative regulation on the expression of the antiapoptotic factor Bcl-2 (72), and on the synthesis of the growth inhibitor transforming growth factor-ß (73, 74, 75). Androgens also stimulate IGF-binding protein (IGFBP)-5 synthesis and indirectly affect IGF-I action. Likewise, by inhibiting the enzyme neutral endopeptidase, AR may indirectly control neuropeptide-induced PC cell growth (76). Recently, the role of androgen in angiogenesis modulation has also been explored and data relevant to PC treatment have emerged (77, 78, 79, 80).

AR amplification is rarely found in primary cancer but is common in recurrent therapy-resistant cancer [20% (81), 30%, (82)]. Thus, the androgen-deprived environment may favor clonal expansion of cancer cells expressing a high level of AR due to gene amplification. AR amplification is frequent in cancer that had prolonged (>12 month) response to the initial androgen deprivation therapy (81). It is also associated with favorable treatment response to second-line combined androgen blockade (CAB), longer survival times, and a higher level of PSA expression (81, 83, 84). Taken together, these findings suggest that PCs with AR amplification and overexpression of wild-type AR have survival advantage in androgen-deficient environment. Yet, they are also more differentiated, as evident from their high PSA expression, and, therefore, exhibit better and longer responses to antiandrogen therapies.

A parallel mechanism for progression to AI is afforded by mutation of the AR gene. Over 300 (374, last counted in 1999) somatic and germ line mutations have been described in AR-related diseases (Ref. 85 ; http://www.mcgill.ca/androgendb/, ftp.ebi.ac.uk/pub/databases/androgen, http://www.MC33@musica.mcgill.ca). They affect both the coding and 5' and 3' untranslated regions of the AR gene. In PC, a mutation hot spot in exon 5 of the AR gene has been identified (85). Unlike loss-of-function mutations found in the androgen insensitivity syndrome or spinal and bulbar muscular atrophy, PC-associated AR mutations often bestow the receptor with hypersensitivity, promiscuous usage of ligands, and gain-of-function (86, 87, 88, 89, 90, 91, 92, 93). These mutational changes, in general, either permit the receptor to be trans-activated by lower concentrations of androgen, by antiandrogens, and by nonandrogenic ligands. PCs with mutant receptors are, therefore, better apt to survive an androgen-deprived environment (52). In comparison, mutations that cause inactivation of AR are rare. One study, however, revealed that 22% of cases of latent carcinoma in Japanese men contained inactivating mutations of the AR gene, whereas these mutations were not found in latent cancer in American men. Based on these findings, it has been postulated that inactivating mutations may prevent progression of early cancer in Japanese men (94).

Overall, the frequency of AR mutation in localized PC is low (88, 95, 96) but increased with increasing stage even before androgen ablation therapy (96, 97, 98, 99). These findings suggest that AR mutation is perhaps not a causative factor of tumor initiation but occurs before androgen deprivation therapy rather than as a result of the therapy. Androgen deprivation therapy may provide a selective environment for clones with mutations. In support of the latter theory, AR mutations are commonly found in metastatic cancers following androgen ablation therapy, particularly if an antiandrogen has been used (88, 100, 101, 102). Intriguingly, the types of mutation found in the hormone refractory cancers seem to be dependent on the kind of hormonal therapies given to the patients. For example, Taplin et al. (102) have recently reported a high incidence of AR mutations that can be stimulated by flutamide in bone metastasis obtained from patients who received CAB with flutamide, but not in specimens from patients treated with androgen ablation monotherapy. An important lesson to learn from this data are that any antiandrogen therapy could contribute to tumor progression by exerting selective pressure for clones with AR mutations that bequeath growth advantages in the environment induced by treatment. The promiscuous nature of some mutated ARs in PC raises concerns regarding the use of megestrol acetate (MA), a progestational antiandrogen, and minidose diethylstilbestrol (DES) as alternative programs for androgen blockade (5). It does not seem, however, that patients with AR mutations have a shorter survival than those without AR mutations. Lastly, AR mutation may be a mechanism for acquiring novel phenotypes for clonal establishment in distant metastasis sites.

The polyglutamine region, encoded by CAG repeats, in exon 1 of the AR is polymorphic, and its length (8–31 repeats) is inversely correlated with trans-activation of the receptor, with 40 or more repeats being associated with androgen insensitivity (54). Because the majority of PCs are AR positive, polymorphic differences or mutational changes in polyglutamine length may affect cancer risk and clinical progression. Short CAG repeat length (<22) polymorphism is associated with increased PC risk (103, 104). These alleles are most commonly found in African-American males (75% with short alleles; median length, 18), less frequent in European-Americans (62% with short alleles; median length, 21), and least common in Asian-Americans (49% with repeat short alleles; median length, 22). Thus, AR with shorter CAG repeat lengths are more prevalent in racial groups with higher PC risk. Short CAG repeat lengths also correlate with early onset of PC (105, 106), suggesting that early tumorigenesis is dependent on a more active AR. Other exon 1 AR polymorphisms, the GGN- and GGC-repeat lengths, may also influence PC risk (103, 107, 108, 109), but the functional significance of these polymorphisms is currently unknown. Somatic reduction in glutamine repeats from 24 in nontumor tissues to 18 residues cancer was found in one patient (110). Interestingly, this patient also had an agonistic response to flutamide, suggesting alteration in the length of the polyglutamine stretch may influence trans-activational potential of antiandrogens. A possible mechanism for this to occur may be due to an influence of the CAG repeat size on coregulator interaction with the N-terminal domain of AR (111). An epidemiologic study showed that germ line shortening of the CAG repeat length correlated with advanced clinical stage and poor prognosis (112).

Another important mechanism of PC progression involves ligand-independent activation of AR by growth factors such as IGF-I, keratinocyte growth factor (KGF), epidermal growth factor (EGF), and by cellular signaling regulators such as cAMP, butyrate, interleukin 6, bombesin, and activators of the protein kinase A signaling pathways (113, 114, 115, 116). One or more of these pathways may prove to be an important mechanism sustaining androgen-dependent PC growth after castration or LH-releasing hormone (LHRH) analog treatment. The fact that AR continues to be expressed or even up-regulated in advanced PC provides evidence that AR remains functionally active either in a ligand-dependent or ligand-independent manor (81, 117).

It has now become apparent that the trans-activational activity of a steroid receptor such as the AR is dependent on interaction with receptor-specific or general coregulators (118). Recently identified AR-specific coregulators include ARA54, ARA55, ARA24, ARA 160, and FLH2 (119, 120). Other more general steroid receptor coregulators such as CBP, SRC-1, ARA70, and TRAM-1 as well as oncogenic molecules such as BRCA-1, RB, and Her2/neu have been demonstrated to influence AR trans-activation (118). Altered regulation or mutation of coactivators is a potential mechanism for altered PC growth. The presence of coactivator abnormalities and their functional significance to PC progression are under intense investigation.

In summary, the genesis and progression of PC likely requires a wild-type AR. ARs with higher trans-activating potentials are promotional for these events. Thus, polymorphic differences or mutation-induced contraction of the polyglutamine repeat in exon 1, mutations that leads to hypersensitivity or gain in function of the receptor, and gene amplification are all probable mechanisms for cancer progression. Androgen deprivation therapy introduces new selection criteria for clones expressing different AR phenotypes, and modifies the AR status of the cancers. Ligand-independent AR activation and altered modulations of AR trans-activation by coregulators are likely involved in promoting progression of androgen-dependent PC to an AI state.

Involvement of other hormonal factors

Hormone receptors other than AR may be involved in PC biology. An analysis of estrogen receptor (ER)-{alpha} and -ß in normal prostate, dysplasia, cancer, and hormone refractory PC (HRPC) has demonstrated expression of ER-ß in HRPC (121). In the PC cell lines PC-3 and DU0145, ICI 182,780, a selective ER antagonist was able to inhibit growth. This inhibition was abrogated by an ER-ß antisense oligonucleotide (122). Future trials will explore the use of ICI 182,780 in HRPC.

Specific polymorphisms in the vitamin D receptor gene have been identified to offer protection against PC and influence PC susceptibility (123, 124). 1,25-Dihydroxyvitamin D3 deficiency has been implicated in the genesis of prostatic cancer (125). This active metabolite of vitamin D maintains differentiation of prostate epithelial cells and retards the development of PC. In vitro 1,25-dihydroxyvitamin D3 was able to inhibit PC growth in both an androgen-dependent and androgen-independent manner (126). In addition, despite initial concerns regarding potential hypercalcemia, vitamin D analogs are being tested in clinical trials (127).

PRL, GH, and LH, acting alone or in concert with androgens, are known to regulate normal physiological functions of the prostate (128). Recent experimental and clinical data now show that they may play important roles in PC development and progression (129, 130, 131, 132). Future investigations evaluating hormones as etiological factors in PC development need to address the roles of these hormones. Mechanisms responsible for prostate carcinogenesis and the development of HRPC are likely diverse, however, an understanding of hormone-controlled growth factors and cell cycle regulators will hopefully advance therapeutics beyond castration (Table 1Go).

PC diagnosis and local treatment

With the use of PSA for early diagnosis and the transrectal ultrasound for prostate biopsy, the majority of PCs are now diagnosed before overt metastases. The PSA gene, located on chromosome 19 was cloned in 1987 (133). PSA is a member of the kallikrein gene family (14 members) and functions as a serine protease. PSA expression is primarily limited to prostate epithelial cells, although some expression has been observed in benign and malignant breast cells (134). In the serum, PSA is bound to {alpha}-1-antichymotrypsin. For unclear reasons, more PSA is bound to {alpha}-1-antichymotrypsin in PC compared with benign prostate enlargement (BPH). The free PSA to total PSA ratio (<18%) can improve diagnostic specificity by 20% when the serum PSA is elevated in the range of 4–10 (135). The total PSA, percent-free PSA, and digital rectal examination will guide the recommendation for prostate biopsy, however, the diagnosis of PC can be difficult and may require more than one biopsy series.

PSA expression is regulated by AR. PSA is an outstanding tumor marker; a possible role for PSA in carcinogensis is under active investigation (136). There have been reports suggesting that PSA may play a beneficial role to inhibit PC growth as well as reports demonstrating that PSA may actually stimulate growth (137, 138). These conflicting results likely stem from the limitations of in vitro cell line work, nonphysiolgic enzyme concentrations and impurities (136). Further investigation may prove the usefulness of PSA as a therapeutic target. Androgen-regulated genes are diverse and together with PSA include many important growth factors and cell cycle regulators (58). Androgens stimulate the expression of EGF receptor, KGF, NEP, ARA 70, CDK 2 and 4, p21, hGK 2, fatty acid synthase, PSA, vascular endothelial growth factor, and IGFBP-5. Androgens repress the expression of transforming growth factor-ß, p16, and bcl-2. There can be either stimulation or inhibition of p27 and IGFBP-5. The balance between these androgen-regulated factors continues to be investigated in the context of PC initiation and progression.

At the time of diagnosis patients are usually stratified into low risk vs. high risk of recurrence based on descriptive features. Risk factors for recurrence include a Gleason score of 7 higher, PSA of 10 or more, and stage T2 (palpable nodule) or greater (139). Therapies are based on these prognostic factors, together with the patients age and general health. In the future, gene chip technology may provide a more accurate biologic profile to guide management.

When cancer is localized to the prostate, standard treatment options include prostatectomy and radiation delivered either by conformal external beam radiation therapy (EBRT) or brachytherapy I125 or palladium (103). The addition of medical castration (see below, primary hormone therapy) to prostatectomy and prostate radiation has had a divergent impact on outcomes. Three months of medical castration before prostatectomy improved pathologic tumor stage and margin status, but there was no improvement in disease-free or overall survival and, therefore, is not routinely recommended (140). In contrast, medical castration in conjunction with EBRT has become standard care for locally advanced or high-grade tumors (141). In a European cooperative group trial, Bolla et al. (141) compared 3 yr of medical castration plus EBRT to ERBT alone. They demonstrated a 37% improvement in disease-free survival and 12% improvement in overall survival at 5 yr for combined hormone/EBRT (141). The lack of benefit for hormone therapy with surgery compared with radiation may result from the divergent duration of hormones used (3 months vs. 3 yr). In fact, the optimal duration of hormone therapy with EBRT is presently unknown and being investigated in the context of clinical trials.

The biology of the interaction of castration combined with EBRT is also under investigation. A retrospective analysis of tumor from patients randomized to EBRT with or without 6 months of hormone therapy in RTOG 8610 suggested that prostate tumors required a wild-type p53 to benefit from combined therapy (142). If p53 status correlates with response in larger prospective analyses, p53 could be a future target for gene therapy in PC.

Adjuvant therapy

Unlike breast cancer, there is no proven benefit for adjuvant hormone therapy in localized (lymph node-negative) PC. A large trial, completed by AstraZeneca, randomized postprostatectomy patients to 2 yr of the antiandrogen bicalutamide (casodex, 150 mg) vs. placebo. This trial was composed of three separate studies with somewhat different entry criteria in the United States, Europe, and Scandinavia. The published results of these trials are not yet available, but early evaluation in the European and Scandinavian trials seems to show reduction in time to progression. Survival cannot yet be assessed. With further follow-up if benefit is confirmed, the prescription of adjuvant antiandrogen therapy may become standard for PC. The national clinical trials cooperative groups have taken a similar but more aggressive approach to adjuvant therapy. Men at high risk for failure after prostatectomy are randomized to 2 yr of CAB therapy with a GnRH agonist and antiandrogen vs. CAB plus six cycles of mitoxantrone chemotherapy. If proven beneficial, this approach will be analogous to the use of adjuvant ER antagonists and chemotherapy in breast cancer.

Primary hormone therapy (Table 2Go)

Castration, commonly referred to as "hormone therapy," is standard first-line therapy for advanced PC. Castration was initially accomplished by orchiectomy or DES. DES, although very affordable, fell out of favor because of cardiac toxicity and is no longer routinely available in the United States. GnRH analogs are available as agonists and antagonists. The GnRH agonists have been in clinical practice since 1985. The agonists provide a castrate level of T by desensitizing the pituitary to native GnRH stimulation. The availability of 3- to 4-month depot preparations of GnRH analogs has allowed this method of castration to become the preferred treatment for many patients. A 1-yr depot preparation of lupron is also now available. Recently, a GnRH antagonist has completed Phase III testing and is awaiting approval for routine clinical use. Castrate T levels are obtained immediately without potential risk of T flare with GnRH antagonist compared with approximately 3 weeks to obtain castration with GnRH agonists (143).


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Table 2. Methods of initial castration therapy for the hormonal treatment of prostate cancer

 
In the United States the choices for initial castration are expanding. The antiandrogen bicalutamide (Casodex) at a dose of 150 mg daily has been evaluated but not approved for first-line therapy (144). This approach has less impotence but more gynecomastia and, with the power to detect a 25% difference compared with standard GnRH therapy, seemed equally efficacious. The other approach under investigation for first-line hormone therapy for advanced PC is intermittent hormone therapy (145). With the intermittent approach, the GnRH analog is given for approximately 7 months, and if the PSA is less than 4 ng/dl, then patients are randomized to continuous vs. intermittent therapy (CALGB 9594/SWOG 9346). The patients on the intermittent therapy are restarted on GnRH analog when the PSA reaches 20 ng/dl. This method of administering GnRH analogs could reduce side effects, cost, and, theoretically, prolong time to progression if abrogation of castration reduces selective pressure for AI clones.

Because of the availability of PSA for following PC, castration therapy, which traditionally was reserved for symptomatic metastatic disease, is being used earlier in the natural history of the disease. A recent study demonstrated benefit for prostatectomy plus castration compared with prostatectomy alone for patients with involved lymph nodes (146). Castration therapy, however, is not curative, and within a variable time period (18–48 months) the majority of patients will demonstrate escape from therapy with a rising PSA. The molecular mechanisms responsible for hormone independence, which have been discussed above, are not fully known and are likely heterogeneous.

Before discussing second-line hormone options, castration by monotherapy and CAB will be defined. Monotherapy is the use of orchiectomy or GnRH analog alone, and CAB includes one of these plus an antiandrogen. Antiandrogens function at the cellular level by binding to HSP and preventing activation of AR (147). Theoretically, antiandrogens, when combined with testicular suppression, can block stimulation from adrenal androgens that contribute approximately 5–10% of total T. A prospective trial comparing GnRH analog alone or with flutamide suggested a survival benefit for CAB, especially for patients with limited metastatic disease (148). A recent well-powered prospective study, however, showed no survival benefit for the addition of an antiandrogen to orchiectomy (149). Survival was no better despite the fact that 74% of the CAB group had a nadir PSA of less than 4 ng/dl compared with 61% of the orchiectomy group (149). Most practitioners, therefore, recommend orchiectomy alone, but some debate continues for the initial use of an antiandrogen with a GnRH analog.

Second-line hormone therapy (Table 3Go)

Previous dogma held that, unlike breast cancer, once PC escaped from initial castration there were no further effective therapeutic hormonal options. There has been renewed interest in and demonstrated benefit for second-line hormone therapies for PC (150). This interest has been driven by multiple factors, including patient preference for change in therapy when the PSA starts to rise despite no clinical symptoms and patient and physician reluctance to use chemotherapy early. It should be noted, however, that there have been no clinical trials to assess survival benefit for secondary hormonal therapies or to assess the proper sequence to prescribe these treatments.


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Table 3. Methods of second-line hormone therapy for PC

 
Castration is typically defined as a serum T level less than 35–50 ng/dl. The normal range for serum T is 240–828 ng/dl. When a patient starts to escape first-line hormone therapies for nonsurgical castration, it is prudent to document a castrate level of T. If the patient is on a therapy such as an antiandrogen alone, which does not induce a castrate level of T, the first step to consider is to lower the T to castrate levels with either orchiectomy or an GnRH analog.

Patients treated with CAB should have the antiandrogen discontinued when the PSA starts to rise. Kelly and Scher (151) were the first to report a series of patients who had a withdrawal response when flutamide was stopped. In their series of 35 patients, 29% showed a greater than 80% decline in PSA, pain improved, and there was documented improvement in measurable disease in two patients. The average duration of response was 5+ months, and the average duration of prior flutamide exposure was 14 months. Additional investigators have documented flutamide withdrawal response rates ranging from 15–80% for an overall response rate of 35% (96 of 276) (152). The withdrawal response has also been reported in smaller numbers of patients on bicalutamide, megestrol, DES, cypertone acetate, estramustine, and 13-cis-retinoic acid (152).

It has been theorized that the antiandrogen withdrawal syndrome is the result of point mutations in the hormone-binding domain of the AR (153). These types of AR mutations have been found from clinical PC specimens (91, 96, 102). The mutations allow activation of the receptor by a range of nonphysiologic ligands including flutamide, progesterone, estrogen, and cortisol (90, 93). To date, however, there has not been direct correlation of mutations with antiandrogen withdrawal. In fact, abstracted results from a Cancer and Leukemia group B (CALGB) trial of simultaneous vs. sequential antiandrogen withdrawal and adrenal blockade with AR analysis from bone marrow metastases did not show a correlation of AR mutation with antiandrogen withdrawal (154). It has become standard care when the PSA starts to rise on CAB to discontinue the antiandrogen and observe for withdrawal response. It is recommended based on drug half-life to observe the patient for 1 month after flutamide discontinuation and for 2 months after stopping bicalutamide. This observation period will prevent confusion regarding responses to subsequent therapy.

The addition of a first or second (after discontinuation of first) antiandrogen when the PSA begins to rise is common practice. There have been two Phase II trials evaluating the use of second-line bicalutamide (150 mg daily) (155, 156). In both of these trials response was correlated with prior exposure to flutamide. There was a 38–43% response (PSA decline, >50%) for patients previously treated with flutamide compared with 6–15% response with no prior flutamide. The average duration of response was 5 months, although one patient who started second-line bicalutamide with a PSA of 18 remains in clinical and serologic remission at 60 months (155).

There are anecdotal reports of patients responding to a third antiandrogen although the response rate is likely low (<10%) and of brief duration. The three antiandrogens approved for use in the United States—flutamide, bicalutamide, and nilutamide—all function by binding to AR-associated HSPs and preventing AR from binding to T or DHT (157). Mechanistically, therefore, it is unclear why some tumors will be sequentially inhibited.

At this point, no clear recommendation can be made regarding the proper sequence of and number of antiandrogens to use as second-line therapy. Practice is frequently governed by convenience and reimbursement issues. Future clinical trials will hopefully provide guidance.

Inhibition of adrenal androgen synthesis has reported response rates of between 19–44% as second-line therapy in PC (158). Adrenalectomy and hypophysectomy are no longer used to reduce adrenal androgens because of the associated morbidity. There are three options for inducing a medical adrenalectomy: aminoglutethimide, ketoconazole, and hydrocortisone. Aminoglutethimide was initially developed as an anticonvulsant and subsequently found to cause adrenal insufficiency. Ketokonazole is an antifungal agent that was found to cause gynecomastia. Both drugs inhibit adrenal androgen synthesis by blocking adrenal hydroxylases and aromatases (159). Aminoglutethimide (250 mg four times a day) and ketoconazole (400 mg three times a day) are often combined with hydocortisone to prevent addisonian symptoms. Studies have suggested that the combination of aminoglutethimide and hydrocortisone was no more effective than hydrocortisone alone, which is a potent inhibitor of adrenal androgen production (160).

Two Phase II trials have reported a response rate of 44–55% for the combination of antiandrogen withdrawal and simultaneous adrenal blockade (161, 162). As mentioned above, the CALGB cooperative clinical trials group has recently completed a randomized trial evaluating combination vs. sequential maneuvers. Results to be presented at the 2001 American Society of Oncology meeting reveal no significant improvement or survival for combining antiandrogen withdrawal with simultaneous adrenal blockade. Insight into the effectiveness of sequential therapy can be obtained from another trial recently competed at the University of Massachusetts Medical Center (Worcester, MA) and Beth Israel Deaconess hospitals (Boston, MA). This Phase II trial demonstrated no response to adrenal blockade for patients progressing on second-line bicalutamide (150 mg) (Bubley, G. J., S. P. Balk, and M. E. Taplin, submitted for publication). This small trial suggests that when patients had failed primary hormone therapy and the AR remained blocked with bicalutamide, further reduction in adrenal androgens was of no benefit.

DES has been evaluated as second-line hormone therapy in PC. One reported mechanism of action for DES in patients treated with orchiectomy or GnRH agonist is suppression of adrenal androgens (163), and another is induction of tumor cell apoptosis (164). In a Phase II trial of DES (1 mg) in 21 patients there was a 43% PSA (50% decline) overall response rate (165). Patients with only one previous hormone therapy responded 62% compared with 13% of patients who had two or more hormone treatments. No anticoagulation was used, and there was one (5%) deep venous thrombosis. In a Canadian trial of DES (1, 2, or 3 mg) combined with coumadin (1 mg) there was an unacceptable toxicity with 31% deep venous thrombosis, 7% myocardial infarction, 7% transient ischemic attacks, and one patient with angina or congestive heart failure (166). In clinical practice the use of DES is limited by its potential toxicity and limited availability outside clinical trials.

Another form of estrogen is the herbal preparation PC-SPEC. PC-SPEC contains eight herbs and has estrogenic activity (167). PC-SPEC has demonstrated activity in hormone-sensitive PC, reducing T and PSA (167). PC-SPEC-induced castration has the same morbidity as traditional castrating agents but, because of its herbal nature, has gained popularity among patients. The effectiveness of PC-SPEC in the second-line setting is presently under investigation. Early results of a Phase II trial of PC-SPEC in 23 patients demonstrated a PSA response (>50% decline) of 52% with a median duration of response of 2.2 months (range, 1–7) (168). Practical issues pertaining to this compound include lack of standardization of active compounds in PC-SPEC and the cost because it is not covered by insurance plans.

Hormonal agents that have shown minimal effectiveness as second-line therapy include MA and tamoxifen. A CALGB trial randomized 149 patients to either 160 mg or 640 mg MA (169). There was no survival benefit for the high-dose arm, and only 14% of all men had a greater than 50% drop in PSA. Similarly, in a Phase II study of tamoxifen in 30 patients there was only one partial response (170). These agents, therefore, cannot be recommended enthusiastically for consideration as second-line therapy.

Many patients with PC will have disease responsive to second-line hormone therapies. The clinician should first document a castrate level of T and direct therapy to reduce T if it is not in the castrate range. A sequential approach to the second-line options discussed above can then be initiated. Responding patients may benefit for months to years from second-line hormone therapies. The duration of response will likely shorten with each subsequent hormone maneuver. This approach is rational because at this time, although chemotherapy has high response rates, there has been no demonstrated benefit for early chemotherapy. More effective hormonal and targeted biologic approaches will likely develop as our understanding of the molecular and cellular mechanisms of PC evolves.

Summary

Mechanisms responsible for prostate carcinogenesis and the development of HRPC are diverse. As our understanding of hormone-controlled growth factors and cell cycle regulators expands, targeted therapeutics will move beyond standard castration and improve the length and quality of life for PC patients.

Footnotes

This work was supported by NIH Grants CA15776 and CA62269 and Department of Defense Grant DAMD17-98-1-8606 (to S.-M.H.).

Abbreviations: aa, Amino acid; AI, androgen independence; AR, androgen receptor; BPH, benign prostatic hyperplasia; CAB, combined androgen blockade; CALGB, Cancer and Leukemia group B; DES, diethylstilbestrol; DHEA, dehydroepiandrosterone; DHT, 5{alpha}-dihydrotesterone; E2, estradiol; EBRT, external beam radiation therapy; EGF, epidermal growth factor; ER, estrogen receptor; HRPC, hormone-refractory prostate cancer; HSP, heat shock protein; IGFBP, IGF-binding protein; KGF, keratinocyte growth factor; LHRH, LH-releasing hormone; MA, megestrol acetate; PC, prostate cancer; PSA, prostate-specific antigen; SHBG, sex hormone-binding globulin; T, testosterone; TAF, transcriptional activation function.

Received January 4, 2001.

Accepted April 29, 2001.

References

  1. Greenlee RT, Murray T, Bolden S, Wingo PA 2000 Cancer statistics, 2000. CA Cancer J Clin 50:7–33[Abstract/Free Full Text]
  2. Huggins C, Hodges CV 1941 The effect of castration, of oestrogen and of androgen injections on serum phosophatases in metastatic carcinoma of the prostate. Cancer Res 1:293–297
  3. Coffey DS 1992 The molecular biology, endcrinology and physiology of the prostate and seminal vesicles. In: Walsh PC, Retik AB, Stamey TA, Vaughn JED, eds. Campbell’s urology, ed. 6. W. B. Saunders Co.; 1381–1428
  4. Cheng E, Lee C, Aaronson SA, Grayhack J 1993 Endocrinology of the prostate. In: Lepor H, Lawson RE, eds. Prostate disease. W. B. Saunders Co.; 57–71
  5. Geller J, de la Vega DJ, Albert JD, Nachtsheim DA 1984 Tissue dihydrotestosterone levels and clinical response to hormonal therapy in patients with advanced prostate cancer. J Clin Endocrinol Metab 58:36–40[Abstract]
  6. Vermeulen A 1973 The physical state of testosterone in plasma. In: James VHT, Serio M, Maratini L, eds. The endocrine function of the htestis. New York: Academic Press; 157–170
  7. Labrie F, Sugimoto Y, Luu-The V, et al. 1992 Structure of human type II 5 {alpha}-reductase gene. Endocrinology 131:1571–1573[Abstract]
  8. Bartsch G, Rittmaster RS, Klocker H 2000 Dihydrotestosterone and the concept of 5{alpha}-reductase inhibition in human benign prostatic hyperplasia. Eur Urol 37:367–380[CrossRef][Medline]
  9. Bruchovsky N, Sadar MD, Akakura K, Goldenberg SL, Matsuoka K, Rennie PS 1996 Characterization of 5{alpha}-reductase gene expression in stroma and epithelium of human prostate. J Steroid Biochem Mol Biol 59:397–404[CrossRef][Medline]
  10. Brawley OW, Parnes H 2000 Prostate cancer prevention trials in the USA. Eur J Cancer 36:1312–1315[CrossRef][Medline]
  11. Simpson E, Rubin G, Clyne C, et al. 1999 Local estrogen biosynthesis in males and females. Endocr Relat Cancer 6:131–137[Abstract/Free Full Text]
  12. Matzkin H, Soloway MS 1992 Response to second-line hormonal manipulation monitored by serum PSA in stage D2 prostate carcinoma. Urology 40:78–80[Medline]
  13. Tsugaya M, Harada N, Tozawa K, et al. 1996 Aromatase mRNA levels in benign prostatic hyperplasia and prostate cancer. Int J Urol 3:292–296[Medline]
  14. Hiramatsu M, Maehara I, Ozaki M, Harada N, Orikasa S, Sasano H 1997 Aromatase in hyperplasia and carcinoma of the human prostate. Prostate 31:118–124[CrossRef][Medline]
  15. Sciarra F, Toscano V 2000 Role of estrogens in human benign prostatic hyperplasia. Arch Androl 44:213–220[CrossRef][Medline]
  16. Wilson CM, McPhaul MJ 1994 A and B forms of the androgen receptor are present in human genital skin fibroblasts. Proc Natl Acad Sci USA 91:1234–1238[Abstract]
  17. Guinan PD, Sadoughi W, Alsheik H, Ablin RJ, Alrenga D, Bush IM 1976 Impotence therapy and cancer of the prostate. Am J Surg 131:599–600[Medline]
  18. Jackson JA, Waxman J, Spiekerman AM 1989 Prostatic complications of testosterone replacement therapy. Arch Intern Med 149:2365–2366[Abstract]
  19. Roberts JT, Essenhigh DM 1986 Adenocarcinoma of prostate in 40-year-old body-builder [Letter]. Lancet 2:742
  20. Driscoll SG, Taylor SH 1980 Effects of prenatal maternal estrogen on the male urogenital system. Obstet Gynecol 56:537–542[Abstract]
  21. Ho SM, Lee KF, Lane K 1997 Neoplastic transformation of the prostate. In: Naz RK, ed. Prostate: basic and clinical aspects. New York: CRC Press Boca Raton; 74–114
  22. Bosland MC 2000 The role of steroid hormones in prostate carcinogenesis [In Process Citation]. J Natl Cancer Inst Monogr 27:39–66[Medline]
  23. Comstock GW, Gordon GB, Hsing AW 1993 The relationship of serum dehydroepiandrosterone and its sulfate to subsequent cancer of the prostate. Cancer Epidemiol Biomark Prev 2:219–221[Abstract]
  24. Dorgan JF, Albanes D, Virtamo J, et al. 1998 Relationships of serum androgens and estrogens to prostate cancer risk: results from a prospective study in Finland [published erratum appears in Cancer Epidemiol Biomark Prev 1999 May, 8:485]. Cancer Epidemiol Biomark Prev 7:1069–1074
  25. Gann PH, Hennekens CH, Ma J, Longcope C, Stampfer MJ 1996 Prospective study of sex hormone levels and risk of prostate cancer [see comments]. J Natl Cancer Inst 88:1118–1126[Abstract/Free Full Text]
  26. Hsing AW, Comstock GW 1993 Serological precursors of cancer: serum hormones and risk of subsequent prostate cancer. Cancer Epidemiol Biomark Prev 2:27–32[Abstract]
  27. Nomura A, Heilbrun LK, Stemmermann GN, Judd HL 1988 Prediagnostic serum hormones and the risk of prostate cancer. Cancer Res 48:3515–3517[Abstract]
  28. Gray A, Feldman HA, McKinlay JB, Longcope C 1991 Age, disease, and changing sex hormone levels in middle-aged men: results of the Massachusetts Male Aging Study. J Clin Endocrinol Metab 73:1016–1025[Abstract]
  29. Krieg M, Nass R, Tunn S 1993 Effect of aging on endogenous level of 5 alpha-dihydrotestosterone, testosterone, estradiol, and estrone in epithelium and stroma of normal and hyperplastic human prostate. J Clin Endocrinol Metab 77:375–381[Abstract]
  30. Ross R, Bernstein L, Judd H, Hanisch R, Pike M, Henderson B 1986 Serum testosterone levels in healthy young black and white men. J Natl Cancer Inst 76:45–48[Medline]
  31. de Jong FH, Oishi K, Hayes RB, et al. 1991 Peripheral hormone levels in controls and patients with prostatic cancer or benign prostatic hyperplasia: results from the Dutch-Japanese case-control study. Cancer Res 51:3445–3450[Abstract]
  32. Ross RK, Bernstein L, Lobo RA, et al. 1992 5-alpha-reductase activity and risk of prostate cancer among Japanese and U.S. white and black males. Lancet 339:887–889[Medline]
  33. Wu AH, Whittemore AS, Kolonel LN, et al. 1995 Serum androgens and sex hormone-binding globulins in relation to lifestyle factors in older African-American, white, and Asian men in the United States and Canada. Cancer Epidemiol Biomark Prev 4:735–741[Abstract]
  34. Henderson BE, Bernstein L, Ross RK, Depue RH, Judd HL 1988 The early in utero oestrogen and testosterone environment of blacks and whites: potential effects on male offspring. Br J Cancer 57:216–218[Medline]
  35. Hill P, Wynder EL, Garnes H, Walker AR 1980 Environmental factors, hormone status, and prostatic cancer. Prev Med 9:657–666[Medline]
  36. Febbo PG, Kantoff PW, Platz EA, et al. 1999 The V89L polymorphism in the 5{alpha}-reductase type 2 gene and risk of prostate cancer. Cancer Res 59:5878–5881[Abstract/Free Full Text]
  37. Makridakis NM, Ross RK, Pike MC, et al. 1999 Association of missense substitution in SRD5A2 gene with prostate cancer in African-American and Hispanic men in Los Angeles, USA. Lancet 354:975–978[CrossRef][Medline]
  38. Reichardt JK, Makridakis N, Henderson BE, Yu MC, Pike MC, Ross RK 1995 Genetic variability of the human SRD5A2 gene: implications for prostate cancer risk. Cancer Res 55:3973–3975[Abstract]
  39. Lunn RM, Bell DA, Mohler JL, Taylor JA 1999 Prostate cancer risk and polymorphism in 17 hydroxylase (CYP17) and steroid reductase (SRD5A2). Carcinogenesis 20:1727–1731[Abstract/Free Full Text]
  40. Feigelson HS, Shames LS, Pike MC, Coetzee GA, Stanczyk FZ, Henderson BE 1998 Cytochrome P450c17{alpha} gene (CYP17) polymorphism is associated with serum estrogen and progesterone concentrations. Cancer Res 58:585–587[Abstract]
  41. Devgan SA, Henderson BE, Yu MC, et al. 1997 Genetic variation of 3 ß-hydroxysteroid dehydrogenase type II in three racial/ethnic groups: implications for prostate cancer risk. Prostate 33:9–12[CrossRef][Medline]
  42. Verreault H, Dufort I, Simard J, Labrie F, Luu-The V 1994 Dinucleotide repeat polymorphisms in the HSD3B2 gene. Hum Mol Genet 3:384
  43. Evans RM 1988 The steroid and thyroid hormone receptor superfamily. Science 240:889–895[Medline]
  44. O’Malley B 1990 The steroid receptor superfamily: more excitement predicted for the future. Mol Endocrinol 4:363–369[Medline]
  45. Fang S, Anderson KM, Liao S 1969 Receptor proteins for androgens. On the role of specific proteins in selective retention of 17-ß-hydroxy-5-{alpha}-androstan-3-one by rat ventral prostate in vivo and in vitro. J Biol Chem 244:6584–6595[Abstract/Free Full Text]
  46. Chang CS, Kokontis J, Liao ST 1988 Molecular cloning of human and rat complementary DNA encoding androgen receptors. Science 240:324–326[Medline]
  47. Lubahn DB, Joseph DR, Sullivan PM, Willard HF, French FS, Wilson EM 1988 Cloning of human androgen receptor complementary DNA and localization to the X chromosome. Science 240:327–330[Medline]
  48. Faber PW, van Rooij HC, Schipper HJ, Brinkmann AO, Trapman J 1993 Two different, overlapping pathways of transcription initiation are active on the TATA-less human androgen receptor promoter. The role of Sp1. J Biol Chem 68:9296–9301
  49. Tilley WD, Marcelli M, McPhaul MJ 1990 Expression of the human androgen receptor gene utilizes a common promoter in diverse human tissues and cell lines. J Biol Chem 265:13776–13781[Abstract/Free Full Text]
  50. Faber PW, van Rooij HC, van der Korput HA, et al. 1991 Characterization of the human androgen receptor transcription unit. J Biol Chem 266:10743–10749[Abstract/Free Full Text]
  51. Trapman J, Klaassen P, Kuiper GG, et al. 1988 Cloning, structure and expression of a cDNA encoding the human androgen receptor. Biochem Biophys Res Commun 153:241–248[Medline]
  52. Prins GS 2000 Molecular biology of the androgen receptor. Mayo Clin Proc 75(Suppl):S32–S35
  53. Fang S, Anderson KM, Liao S 1969 Receptor proteins for androgens. On the role of specific proteins in selective retention of 17-ß-hydroxy-5-{alpha}-androstan-3-one by rat ventral prostate in vivo and in vitro. J Biol Chem 244:6584–6595[Abstract/Free Full Text]
  54. Chamberlain NL, Driver ED, Miesfeld RL 1994 The length and location of CAG trinucleotide repeats in the androgen receptor N-terminal domain affect transactivation function. Nucleic Acids Res 22:3181–3186[Abstract]
  55. Jenster G, Trapman J, Brinkmann AO 1993 Nuclear import of the human androgen receptor. Biochem J 293:761–768[Medline]
  56. Jenster G, van der Korput HA, Trapman J, Brinkmann AO 1995 Identification of two transcription activation units in the N-terminal domain of the human androgen receptor. J Biol Chem 270:7341–7346[Abstract/Free Full Text]
  57. Jenster G, van der Korput HA, van Vroonhoven C, van der Kwast TH, Trapman J, Brinkmann AO 1991 Domains of the human androgen receptor involved in steroid binding, transcriptional activation, and subcellular localization. Mol Endocrinol 5:1396–1404[Abstract]
  58. Culig Z, Hobisch A, Bartsch G, Klocker H 2000 Androgen receptor—an update of mechanisms of action in prostate cancer [Editorial; In Process Citation]. Urol Res 28:211–219[CrossRef][Medline]
  59. de Winter JA, Trapman J, Brinkmann AO, et al. 1990 Androgen receptor heterogeneity in human prostatic carcinomas visualized by immunohistochemistry. J Pathol 160:329–332[Medline]
  60. Baumann CT, Lim CS, Hager GL 1999 Intracellular localization and trafficking of steroid receptors. Cell Biochem Biophys 31:119–127[CrossRef][Medline]
  61. Trapman J, Cleutjens KB 1997 Androgen-regulated gene expression in prostate cancer. Semin Cancer Biol 8:29–36[CrossRef][Medline]
  62. van der Kwast TH, Schalken J, Ruizeveld de Winter JA, et al. 1991 Androgen receptors in endocrine-therapy-resistant human prostate cancer. Int J Cancer 48:189–193[Medline]
  63. Chodak GW, Kranc DM, Puy LA, Takeda H, Johnson K, Chang C 1992 Nuclear localization of androgen receptor in heterogeneous samples of normal, hyperplastic and neoplastic human prostate. J Urol 147:798–803[Medline]
  64. Masai M, Sumiya H, Akimoto S, et al. 1990 Immunohistochemical study of androgen receptor in benign hyperplastic and cancerous human prostates. Prostate 17:293–300[Medline]
  65. Tilley WD, Lim-Tio SS, Horsfall DJ, Aspinall JO, Marshall VR, Skinner JM 1994 Detection of discrete androgen receptor epitopes in prostate cancer by immunostaining: measurement by color video image analysis. Cancer Res 54:4096–4102[Abstract]
  66. Abrahamsson PA 1999 Neuroendocrine cells in tumour growth of the prostate. Endocr Relat Cancer 6:503–519[Abstract/Free Full Text]
  67. Krijnen JL, Janssen PJ, Ruizeveld de Winter JA, van Krimpen H, Schroder FH, van der Kwast TH 1993 Do neuroendocrine cells in human prostate cancer express androgen receptor? Histochemistry 100:393–398[Medline]
  68. Matsushima H, Goto T, Hosaka Y, Kitamura T, Kawabe K 1999 Correlation between proliferation, apoptosis, and angiogenesis in prostate carcinoma and their relation to androgen ablation. Cancer 85:1822–1827[CrossRef][Medline]
  69. Lu S, Tsai SY, Tsai MJ 1997 Regulation of androgen-dependent prostatic cancer cell growth: androgen regulation of CDK2, CDK4, and CKI p16 genes. Cancer Res 57:4511–4516[Abstract]
  70. Lu S, Liu M, Epner DE, Tsai SY, Tsai MJ 1999 Androgen regulation of the cyclin-dependent kinase inhibitor p21 gene through an androgen response element in the proximal promoter. Mol Endocrinol 13:376–384[Abstract/Free Full Text]
  71. Aaltomaa S, Lipponen P, Eskelinen M, Ala-Opas M, Kosma VM 1999 Prognostic value and expression of p21(waf1/cip1) protein in prostate cancer. Prostate 39:8–15[CrossRef][Medline]
  72. Kolar Z, Murray PG, Scott K, Harrison A, Vojtesek B, Dusek J 2000 Relation of Bcl-2 expression to androgen receptor, p21WAF1/CIP1, and cyclin D1 status in prostate cancer. Mol Pathol 53:15–18[Abstract/Free Full Text]
  73. Kim IY, Kim JH, Zelner DJ, Ahn HJ, Sensibar JA, Lee C 1996 Transforming growth factor-ß1 is a mediator of androgen-regulated growth arrest in an androgen-responsive prostatic cancer cell line, LNCaP. Endocrinology 137:991–999[Abstract]
  74. Kyprianou N, Isaacs JT 1989 Expression of transforming growth factor-ß in the rat ventral prostate during castration-induced programmed cell death. Mol Endocrinol 3:1515–1522[Abstract]
  75. Wikstrom P, Bergh A, Damber JE 2000 Transforming growth factor-ß1 and prostate cancer [In Process Citation]. Scand J Urol Nephrol 34:85–94[CrossRef][Medline]
  76. Sadi MV, Walsh PC, Barrack ER 1991 Immunohistochemical study of androgen receptors in metastatic prostate cancer. Comparison of receptor content and response to hormonal therapy. Cancer 67:3057–3064[Medline]
  77. Jain RK, Safabakhsh N, Sckell A, et al. 1998 Endothelial cell death, angiogenesis, and microvascular function after castration in an androgen-dependent tumor: role of vascular endothelial growth factor. Proc Natl Acad Sci USA 95:10820–10825[Abstract/Free Full Text]
  78. Levine AC, Liu XH, Greenberg PD, et al. 1998 Androgens induce the expression of vascular endothelial growth factor in human fetal prostatic fibroblasts. Endocrinology 139:4672–4678[Abstract/Free Full Text]
  79. Mazzucchelli R, Montironi R, Santinelli A, Lucarini G, Pugnaloni A, Biagini G 2000 Vascular endothelial growth factor expression and capillary architecture in high-grade PIN and prostate cancer in untreated and androgen-ablated patients. Prostate 45:72–79[CrossRef][Medline]
  80. Morris MJ, Scher HI 2000 Novel strategies and therapeutics for the treatment of prostate carcinoma. Cancer 89:1329–1348[CrossRef][Medline]
  81. Moul JW, Srivastava S, McLeod DG 1995 Molecular implications of the antiandrogen withdrawal syndrome. Semin Urol 13:157–163[Medline]
  82. Visakorpi T, Hyytinen E, Koivisto P, et al. 1995 In vivo amplification of the androgen receptor gene and progression of human prostate cancer. Nat Genet 9:401–406[Medline]
  83. Koivisto PA, Helin HJ 1999 Androgen receptor gene amplification increases tissue PSA protein expression in hormone-refractory prostate carcinoma. J Pathol 189:219–223[CrossRef][Medline]
  84. Palmberg C, Koivisto P, Kakkola L, Tammela TL, Kallioniemi OP, Visakorpi T 2000 Androgen receptor gene amplification at primary progression predicts response to combined androgen blockade as second line therapy for advanced prostate cancer [In Process Citation]. J Urol 164:1992–1995[Medline]
  85. Gottlieb B, Beitel LK, Lumbroso R, Pinsky L, Trifiro M 1999 Update of the androgen receptor gene mutations database. Hum Mutat 14:103–114[CrossRef][Medline]
  86. Crocitto LE, Henderson BE, Coetzee GA 1997 Identification of two germline point mutations in the 5'UTR of the androgen receptor gene in men with prostate cancer. J Urol 158:1599–1601[Medline]
  87. Culig Z, Hobisch A, Cronauer MV, et al. 1993 Mutant androgen receptor detected in an advanced-stage prostatic carcinoma is activated by adrenal androgens and progesterone. Mol Endocrinol 7:1541–1550[Abstract]
  88. Ingles SA, Ross RK, Yu MC, et al. 1997 Association of prostate cancer risk with genetic polymorphisms in vitamin D receptor and androgen receptor [see comments]. J Natl Cancer Inst 89:166–170[Abstract/Free Full Text]
  89. Elo JP, Kvist L, Leinonen K, et al. 1995 Mutated human androgen receptor gene detected in a prostatic cancer patient is also activated by estradiol. J Clin Endocrinol Metab 80:3494–3500[Abstract]
  90. Fenton MA, Shuster TD, Fertig AM, et al. 1997 Functional characterization of mutant androgen receptors from androgen-independent prostate cancer. Clin Cancer Res 3:1383–1388[Abstract]
  91. Taplin ME, Bubley GJ, Shuster TD, et al. 1995 Mutation of the androgen-receptor gene in metastatic androgen-independent prostate cancer [see comments]. N Engl J Med 332:1393–1398[Abstract/Free Full Text]
  92. Veldscholte J, Berrevoets CA, Mulder E 1994 Studies on the human prostatic cancer cell line LNCaP. J Steroid Biochem Mol Biol 49:341–346[CrossRef][Medline]
  93. Zhao XY, Malloy PJ, Krishnan AV, Swami S, Navone NM, Peehl DM, Feldman D 2000 Glucocorticoids can promote androgen-independent growth of prostate cancer cells through a mutated androgen receptor. [see comments; published erratum appears in Nat Med 2000 Aug, 6:939]. Nat Med 6:703–706
  94. Takahashi H, Furusato M, Allsbrook Jr WC, et al. 1995 Prevalence of androgen receptor gene mutations in latent prostatic carcinomas from Japanese men. Cancer Res 55:1621–1624[Abstract]
  95. Evans BA, Harper ME, Daniells CE, et al. 1996 Low incidence of androgen receptor gene mutations in human prostatic tumors using single strand conformation polymorphism analysis. Prostate 28:162–171[CrossRef][Medline]
  96. Marcelli M, Ittmann M, Mariani S, et al. 2000 Androgen receptor mutations in prostate cancer. Cancer Res 60:944–949[Abstract/Free Full Text]
  97. Bentel JM, Tilley WD 1996 Androgen receptors in prostate cancer. J Endocrinol 151:1–11[Free Full Text]
  98. Gaddipati JP, McLeod DG, Heidenberg HB, et al. 1994 Frequent detection of codon 877 mutation in the androgen receptor gene in advanced prostate cancers. Cancer Res 54:2861–2864[Abstract]
  99. Tilley WD, Buchanan G, Hickey TE, Bentel JM 1996 Mutations in the androgen receptor gene are associated with progression of human prostate cancer to androgen independence. Clin Cancer Res 2:277–285[Abstract]
  100. Brinkmann AO, Trapman J 2000 Prostate cancer schemes for androgen escape [news; comment]. Nat Med 6:628–629[CrossRef][Medline]
  101. Culig Z, Hobisch A, Hittmair A, et al. 1997 Hyperactive androgen receptor in prostate cancer: what does it mean for new therapy concepts? Histol Histopathol 12:781–786[Medline]
  102. Taplin ME, Bubley GJ, Ko YJ, et al. 1999 Selection for androgen receptor mutations in prostate cancers treated with androgen antagonist. Cancer Res 59:2511–2515[Abstract/Free Full Text]
  103. Irvine RA, Yu MC, Ross RK, Coetzee GA 1995 The CAG and GGC microsatellites of the androgen receptor gene are in linkage disequilibrium in men with prostate cancer. Cancer Res 55:1937–1940[Abstract]
  104. Sartor O, Zheng Q, Eastham JA 1999 Androgen receptor gene CAG repeat length varies in a race-specific fashion in men without prostate cancer. Urology 53:378–380[CrossRef][Medline]
  105. Bratt O, Borg A, Kristoffersson U, Lundgren R, Zhang QX, Olsson H 1999 CAG repeat length in the androgen receptor gene is related to age at diagnosis of prostate cancer and response to endocrine therapy, but not to prostate cancer risk. Br J Cancer 81:672–676[CrossRef][Medline]
  106. Hardy DO, Scher HI, Bogenreider T, et al. 1996 Androgen receptor CAG repeat lengths in prostate cancer: correlation with age of onset. J Clin Endocrinol Metab 81:4400–4405[Abstract]
  107. Correa-Cerro L, Wohr G, Haussler J, et al. 1999 (CAG)nCAA and GGN repeats in the human androgen receptor gene are not associated with prostate cancer in a French-German population. Eur J Hum Genet 7:357–362[CrossRef][Medline]
  108. Platz EA, Giovannucci E, Dahl DM, et al. 1998 The androgen receptor gene GGN microsatellite and prostate cancer risk. Cancer Epidemiol Biomarkers Prev 7:379–384[Abstract]
  109. Stanford JL, Just JJ, Gibbs M, et al. 1997 Polymorphic repeats in the androgen receptor gene: molecular markers of prostate cancer risk [see comments]. Cancer Res 57:1194–1198[Abstract]
  110. Schoenberg MP, Hakimi JM, Wang S, et al. 1994 Microsatellite mutation (CAG24->18) in the androgen receptor gene in human prostate cancer. Biochem Biophys Res Commun 198:74–80[CrossRef][Medline]
  111. Irvine RA, Ma H, Yu MC, Ross RK, Stallcup MR, Coetzee GA 2000 Inhibition of p160-mediated coactivation with increasing androgen receptor polyglutamine length. Hum Mol Genet 9:267–274[Abstract/Free Full Text]
  112. Giovannucci E, Stampfer MJ, Krithivas K, et al. 1997 The CAG repeat within the androgen receptor gene and its relationship to prostate cancer [published erratum appears in Proc Natl Acad Sci USA 1997 July 22, 94:8272]. Proc Natl Acad Sci USA 94:3320–3323[Free Full Text]
  113. Culig Z, Hobisch A, Cronauer MV, et al. 1994 Androgen receptor activation in prostatic tumor cell lines by insulin-like growth factor-I, keratinocyte growth factor, and epidermal growth factor. Cancer Res 54:5474–5478[Abstract]
  114. Jenster G 1999 The role of the androgen receptor in the development and progression of prostate cancer. Semin Oncol 26:407–421[Medline]
  115. Sadar MD 1999 Androgen-independent induction of prostate-specific antigen gene expression via cross-talk between the androgen receptor and protein kinase A signal transduction pathways. J Biol Chem 274:7777–7783[Abstract/Free Full Text]
  116. Sadar MD, Hussain M, Bruchovsky N 1999 Prostate cancer: molecular biology of early progression to androgen independence. Endocr Relat Cancer 6:487–502[Abstract/Free Full Text]
  117. Ruizeveld de Winter JA, Janssen PJ, Sleddens HM, et al. 1994 Androgen receptor status in localized and locally progressive hormone refractory human prostate cancer. Am J Pathol 144:735–746[Abstract]
  118. Robyr D, Wolffe AP, Wahli W 2000 Nuclear hormone receptor coregulators in action: diversity for shared tasks. Mol Endocrinol 14:329–347[Free Full Text]
  119. Muller JM, Isele U, Metzger E, et al. 2000 FHL2, a novel tissue-specific coactivator of the androgen receptor. EMBO J 19:359–369[Abstract/Free Full Text]
  120. Yeh S, Chang HC, Miyamoto H, et al. 1999 Differential induction of the androgen receptor transcriptional activity by selective androgen receptor coactivators. Keio J Med 48:87–92[Medline]
  121. Leav I, Lau KM, Adams JY, et al. Comparative studies of estrogen receptor-ß, {alpha} and androgen receptor in normal human prostate glands, dysplasia and in primary and metastatic carcinoma. Am J Pathol 159:79–92
  122. Lau KM, LaSpina M, Long J, Ho SM 2000 Expression of estrogen receptor (ER)-{alpha} and ER-ß in normal and malignant prostatic epithelial cells: regulation by methylation and involvement in growth regulation. Cancer Res 60:3175–3182[Abstract/Free Full Text]
  123. Correa-Cerro L, Berthon P, Haussler J, et al. 1999 Vitamin D receptor polymorphisms as markers in prostate cancer. Hum Genet 105:281–287[CrossRef][Medline]
  124. Habuchi T, Suzuki T, Sasaki R, et al. 2000 Association of vitamin D receptor gene polymorphism with prostate cancer and benign prostatic hyperplasia in a Japanese population. Cancer Res 60:305–308[Abstract/Free Full Text]
  125. Miller GJ 1998 Vitamin D and prostate cancer: biologic interactions and clinical potentials. Cancer Metastasis Rev 17:353–360[CrossRef][Medline]
  126. Zhao XY, Peehl DM, Navone NM, Feldman D 2000 1alpha,25-dihydroxyvitamin D3 inhibits prostate cancer cell growth by androgen-dependent and androgen-independent mechanisms. Endocrinology 141:2548–2556[Abstract/Free Full Text]
  127. Sporn MB 1999 New agents for chemoprevention of prostate cancer. Eur Urol 35:420–423[CrossRef][Medline]
  128. Reiter E, Hennuy B, Bruyninx M, et al. 1999 Effects of pituitary hormones on the prostate. Prostate 38:159–165[CrossRef][Medline]
  129. Clinton SK, Mulloy AL, Li SP, Mangian HJ, Visek WJ 1997 Dietary fat and protein intake differ in modulation of prostate tumor growth, prolactin secretion and metabolism, and prostate gland prolactin binding capacity in rats. J Nutr 127:225–237[Abstract/Free Full Text]
  130. Horti J, Figg WD, Weinberger B, Kohler D, Sartor O 1998 A phase II study of bromocriptine in patients with androgen-independent prostate cancer. Oncol Rep 5:893–896[Medline]
  131. Leav I, Merk FB, Lee KF, et al. 1999 Prolactin receptor expression in the developing human prostate and in hyperplastic, dysplastic, and neoplastic lesions. Am J Pathol 154:863–870[Abstract/Free Full Text]
  132. Untergasser G, Rumpold H, Hermann M, Dirnhofer S, Jilg G, Berger P 1999 Proliferative disorders of the aging human prostate: involvement of protein hormones and their receptors. Exp Gerontol 34:275–287[CrossRef][Medline]
  133. Lundwall A, Lilja H 1987 Molecular cloning of human prostate specific antigen cDNA. FEBS Lett 214:317–322[CrossRef][Medline]
  134. Lilja H, Piironen TP, Rittenhouse HG, Mikolajczyk SD, Slawin KM 2000 Value of molecular forms of prostate-specific antigen and related kallikrein, hK2, in diagnosis and staging of prostate cancer comprehensive. In: Vogelzang NJ, Scardino PT, Shipley WU, Coffey DS, eds. Textbook of genitourinary oncology. Philadelphia: Lippincott Williams & Wilkins; 000
  135. Oesterling JE, Jacobsen SJ, Klee GG, et al. 1995 Free, complexed and total serum prostate specific antigen: the establishment of appropriate reference ranges for their concentrations and ratios. J Urol 154:1090–1095[Medline]
  136. Diamandis EP 2000 Prostate-specific antigen: a cancer fighter and a valuable messenger? Clin Chem 46:896–900[Abstract/Free Full Text]
  137. Stege R, Grande M, Carlstrom K, Tribukait B, Pousette A 2000 Prognostic significance of tissue prostate-specific antigen in endocrine-treated prostate carcinomas. Clin Cancer Res 6:160–165[Abstract/Free Full Text]
  138. Sutkowski DM, Goode RL, Baniel J, et al. 1999 Growth regulation of prostatic stromal cells by prostate-specific antigen. J Natl Cancer Inst 91:1663–1669[Abstract/Free Full Text]
  139. Partin AW, Piantadosi S, Sanda MG, et al. 1995 Selection of men at high risk for disease recurrence for experimental adjuvant therapy following radical prostatectomy [see comments]. Urology 45:831–838[CrossRef][Medline]
  140. Witjes WP, Schulman CC, Debruyne FM 1997 Preliminary results of a prospective randomized study comparing radical prostatectomy versus radical prostatectomy associated with neoadjuvant hormonal combination therapy in T2–3 N0 M0 prostatic carcinoma. The European Study Group on Neoadjuvant Treatment of Prostate Cancer. Urology 49:65–69
  141. Bolla M, Gonzalez D, Warde P, et al. 1997 Improved survival in patients with locally advanced prostate cancer treated with radiotherapy and goserelin [see comments]. N Engl J Med 337:295–300[Abstract/Free Full Text]
  142. Grignon DJ, Caplan R, Sarkar FH, et al. 1997 p53 status and prognosis of locally advanced prostatic adenocarcinoma: a study based on RTOG 8610. J Natl Cancer Inst 89:158–165[Abstract/Free Full Text]
  143. Sharifi R, Bruskewitz RC, Gittleman MC, Graham Jr SD, Hudson PB, Stein B 1996 Leuprolide acetate 22.5 mg 12-week depot formulation in the treatment of patients with advanced prostate cancer. Clin Ther 18:647–657[CrossRef][Medline]
  144. Boccardo F, Rubagotti A, Barichello M, et al. 1999 Bicalutamide monotherapy versus flutamide plus goserelin in prostate cancer patients: results of an Italian Prostate Cancer Project study. J Clin Oncol 17:2027–2038[Abstract/Free Full Text]
  145. Crook JM, Szumacher E, Malone S, Huan S, Segal R 1999 Intermittent androgen suppression in the management of prostate cancer. Urology 53:530–534[CrossRef][Medline]
  146. Messing EM, Manola J, Sarosdy M, et al. 2000 Immediate hormonal therapy compared with observation after radical prostatectomy and pelvic lymphadenectomy in men with node-postitive prostate cancer. N Eng J Med 341:1781–1788[Abstract/Free Full Text]
  147. Kolvenbag G, Furr BJA, Blacklede GRP 1998 Receptor affinity and potency of non-steroid antiandrogens:translation of preclinical findings into clinical activity. Postate cancer and prostatic diseases 1:307–314
  148. Crawford ED, Eisenberger MA, McLeod DG, et al. 1989 A controlled trial of leuprolide with and without flutamide in prostatic carcinoma [published erratum appears in N Engl J Med 1989 Nov 16, 321:1420]. N Engl J Med 321:419–424
  149. Eisenberger MA, Blumenstein BA, Crawford ED, et al. 1998 Bilateral orchiectomy with or without flutamide for metastatic prostate cancer [see comments]. N Engl J Med 339:1036–1042[Abstract/Free Full Text]
  150. Small EJ, Vogelzang NJ 1997 Second-line hormonal therapy for advanced prostate cancer: a shifting paradigm. J Clin Oncol 15:382–388[Abstract]
  151. Scher HI, Kelly WK 1993 Flutamide withdrawal syndrome: its impact on clinical trials in hormone-refractory prostate cancer. J Clin Oncol 11:1566–1572[Abstract]
  152. Kelly WK, Slovin S, Scher HI 1997 Steroid hormone withdrawal syndromes. Pathophysiology and clinical significance. Urol Clin North Am 24:421–431[Medline]
  153. Culig Z, Hobisch A, Hittmair A, et al. 1997 Androgen receptor gene mutations in prostate cancer. Implications for disease progression and therapy. Drugs Aging 10:50–58[Medline]
  154. Taplin ME, Rajeshkumar B, Woddda BA, et al. Androgen receptor analyses in androgen independent prostate cancer (AIPCA): Cancer and Leukemia group B (CALGB) 9663. Proc ASCO 1997–2000, p 1297 (Abstract)
  155. Joyce R, Fenton MA, Rode P, et al. 1998 High dose bicalutamide for androgen independent prostate cancer: effect of prior hormonal therapy. J Urol 159:149–153[Medline]
  156. Scher HI, Liebertz C, Kelly WK, et al. 1997 Bicalutamide for advanced prostate cancer: the natural versus treated history of disease. J Clin Oncol 15:2928–2938[Abstract]
  157. Veldscholte J, Berrevoets CA, Brinkmann AO, Grootegoed JA, Mulder E 1992 Anti-androgens and the mutated androgen receptor of LNCaP cells: differential effects on binding affinity, heat-shock protein interaction, and transcription activation. Biochemistry 31:2393–2399[Medline]
  158. Shaw MA, Nicholls PJ, Smith HJ 1988 Aminoglutethimide and ketoconazole: historical perspectives and future prospects. J Steroid Biochem 31:137–146[CrossRef][Medline]
  159. Sanford EJ, Paulson DF, Rohner Jr TJ, Santen RJ, Bardin CW 1977 The effects of castration on adrenal testosterone secretion in men with prostatic carcinoma. J Urol 118:1019–1021[Medline]
  160. Plowman PN, Perry LA, Chard T 1987 Androgen suppression by hydrocortisone without aminoglutethimide in orchiectomised men with prostatic cancer. Br J Urol 59:255–257[Medline]
  161. Dawson N, Figg WD, Brawley OW, et al. 1998 Phase II study of suramin plus aminoglutethimide in two cohorts of patients with androgen-independent prostate cancer: simultaneous antiandrogen withdrawal and prior antiandrogen withdrawal. Clin Cancer Res 4:37–44[Abstract]
  162. Small EJ, Baron A, Bok R 1997 Simultaneous antiandrogen withdrawal and treatment with ketoconazole and hydrocortisone in patients with advanced prostate carcinoma. Cancer 80:1755–1759[CrossRef][Medline]
  163. Kitahara S, Umeda H, Yano M, et al. 1999 Effects of intravenous administration of high dose-diethylstilbestrol diphosphate on serum hormonal levels in patients with hormone-refractory prostate cancer. Endocr J 46:659–664[Medline]
  164. Robertson CN, Roberson KM, Padilla GM, et al. 1996 Induction of apoptosis by diethylstilbestrol in hormone-insensitive prostate cancer cells. J Natl Cancer Inst 88:908–917[Abstract/Free Full Text]
  165. Smith DC, Redman BG, Flaherty LE, Li L, Strawderman M, Pienta KJ 1998 A phase II trial of oral diethylstilbesterol as a second-line hormonal agent in advanced prostate cancer [see comments]. Urology 52:257–260[CrossRef][Medline]
  166. Klotz L, McNeill I, Fleshner N 1999 A phase 1–2 trial of diethylstilbestrol plus low dose warfarin in advanced prostate carcinoma. J Urol 161:169–172[Medline]
  167. Hsieh T, Chen SS, Wang X, Wu JM 1997 Regulation of androgen receptor (AR) and prostate specific antigen (PSA) expression in the androgen-responsive human prostate LNCaP cells by ethanolic extracts of the Chinese herbal preparation, PC-SPES. Biochem Mol Biol Int 42:535–544[Medline]
  168. Oh WK, George DJ, Hackman K, Manola J, Kantoff PW 2001 Activity of the herbal combination, PC-SPEC, in the treatment of patients with androgen-independent prostate cancer. Urology 57:122–126[Medline]
  169. Dawson NA, Conaway M, Halabi S, et al. 2000 A randomized study comparing standard versus moderately high dose megestrol acetate for patients with advanced prostate carcinoma: cancer and leukemia group B study 9181. Cancer 88:825–834[CrossRef][Medline]
  170. Bergan RC, Reed E, Myers CE, et al. 1999 A Phase II study of high-dose tamoxifen in patients with hormone- refractory prostate cancer. Clin Cancer Res 5:2366–2373[Abstract/Free Full Text]