Outcome in prostate cancer associations with skin type and polymorphism in pigmentation-related genes

Christopher J. Luscombe1, Michael E. French1, Samson Liu1, Mark F. Saxby1, Peter W. Jones2, Anthony A. Fryer1 and Richard C. Strange3

Department of Urology and
1 Clinical Biochemistry Research Laboratory, School of Postgraduate Medicine, North Staffordshire Hospital, Stoke-on-Trent, Staffordshire and
2 Department of Mathematics, Keele University, UK


    Abstract
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Epidemiological studies have suggested that UV exerts a protective effect on prostate cancer. Accordingly, we determined, in 210 prostate cancer cases, whether parameters of exposure, skin type and polymorphism in MC1R, VDR and TYR were associated with the outcome parameters, histological grade, clinical stage and presence of bone metastases. We used logistic regression analysis, with correction for age and metastases, stage and grade in the models, to determine if the frequencies of individual factors were different in the patient groups. The development of metastases was not associated with UV exposure parameters. Paradoxically, patients with skin type 1 were at significantly reduced risk [P = 0.027, odds ratio (OR) 0.17, 95% CI 0.03–0.82] of developing metastases compared with cases with skin type 4. MC1R Val92/Val92 and VDR ff were associated with increased risk of metastases (ORs 4.30 and 4.98, respectively). Further, cumulative exposure (P = 0.005, OR 0.85/year) and increasing proportion of outdoor occupation (P = 0.001, OR 0.84/unit) were associated with reduced risk of advanced stage tumours. Skin types, MC1R or VDR genotypes were not significantly associated with advanced stage. None of the exposure parameters, skin types or genotypes were associated with tumour grade. While MC1R Val92/Val92 and VDR ff were only associated with bone metastases, TYR genotypes were associated with each of the outcome parameters. Thus, in logistic regression models that included age, but not advanced stage and high grade histology, TYR A1A2 was significantly associated with reduced risk of metastases (P = 0.033, OR 0.41). Similarly, in models that included age but not the other outcome parameters, associations between TYR A2A2 and high-grade and advanced stage were significant (P = 0.040, OR 0.41) or approached significance (P = 0.052, OR 0.44), respectively. These data indicate for the first time that pigmentation response to UV is associated with outcome in prostate cancer.

Abbreviations: CI, confidence intervals; MC1R, melanocyte stimulating hormone receptor; OR, odds ratio; PSA, prostatic specific antigen; TYR, tyrosinase; UV, ultraviolet radiation; VDR, vitamin D receptor.


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Sporadic prostatic adenocarcinoma is a leading cause of morbidity and mortality in men (14). The cancer is generally characterized by a slow clinical course such that disease is only detected at autopsy. Indeed, almost all patients with localized disease at diagnosis will survive at least 5 years. In other subjects, the cancer grows rapidly and demonstrates metastatic spread. Tumour spread is a critical marker of outcome as patients with metastases have a 5 year survival of only 25% (5). The most common site of metastases, after regional lymph node spread, is bone, which is almost invariably involved if there is spread to other organs. The factors that determine individual differences in the development of metastases, clinical T stage and histological grade are poorly understood, though environmental and genetic factors are relevant (14,6). For example, mortality demonstrates marked variation with ethnic group (1,2). Thus, mortality rates in African–Americans are more than twice those of their Caucasian counterparts (4). These findings prompted North American-based studies that linked latitude with prostate cancer mortality and introduced a further factor (8); thus, after controlling for other variables, this association was interpreted as showing that UV is protective against the development of prostate cancer. Other studies provide support for this view (1,2,7). Thus, individual differences in factors that mediate host response to UV, such as skin pigmentation, may influence outcome in this cancer.

Skin colour is largely determined by melanin synthesis (8). The first rate-limiting steps of melanin synthesis are catalysed by the TYR protein product under the influence of melanocyte stimulating hormone (8,9). This hormone acts via receptors including the MC1R. These genes demonstrate functional polymorphisms; some mutations of TYR cause albinism (9) and MC1R variants are linked with hair colour and skin type (8,10,11). Vitamin D is also important. Its metabolites are formed in skin following exposure and can inhibit proliferation of prostate cancer cells (12). Further, associations between VDR genotypes and prostate cancer susceptibility have been reported (13,14).

We now describe studies to determine if parameters of UV exposure determined using a validated questionnaire (15,16), skin type and allelism in MC1R, TYR and VDR are linked with the development of bone metastases, T stage and tumour grade in prostate cancer. These outcome predictors have been shown to have prognostic importance by the American College of Pathologists (17).


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Patients
We recruited (October 1999–May 2000), 210 unrelated, Northern European Caucasian prostate cancer cases in urology clinics in the North Staffordshire Hospital. None of the patients approached refused to participate and the study group includes >85% of cases available between these dates. Data was obtained from all cases on clinical T-stage. Histological evidence (with WHO grade) of prostatic adenocarcinoma was obtained in 190 patients. In 20 severely ill cases with clinically obvious prostate cancer, it was considered unethical to subject patients to the potential morbidity of a biopsy. These cases had a clinically malignant prostate gland on digital rectal examination, positive bone scan and PSA level above 20 ng/ml (age-related reference range up to 6.5 ng/ml). Skin type (types 1–4 in Caucasians) was determined using the Fitzpatrick scale as previously described (18). Type 1 individuals burn on exposure to UV and are unable to tan while type 4 individuals never burn and tan easily. Radionuclide scintigraphy was used to identify bone metastases and was performed in 182 cases on whom the main analysis is based. The mean age of these patients was 70.4 ± 7.5 (SD) years (range 44.3–91.1 years). 90.7% of these patients were aged more than 60 years. Scintigraphy was not performed on 28 cases because the results would not have affected management. Of these, 10 patients (all with histological evidence of prostatic adenocarcinoma) had PSA values <10 ng/ml suggesting the absence of metastases, 8 cases had clinically evident metastases with markedly raised PSA levels and the remaining 10 patients were elderly with no metastatic symptoms. The North Staffordshire Hospital Ethics Committee approved the study and all patients gave informed consent.

Assessment of UV exposure
A validated questionnaire (15,16) was used to determine the following. (i) Childhood sunburning, defined as erythema for more than 48 h or blistering (scored yes/no). (ii) Sunbathing score recorded as never, rare, occasional and frequent (scored 1, 2, 3 and 4 units, respectively) in age categories (20–39, 40–59 and >=60 years). The cumulative score was obtained by adding the units from the three age categories. (iii) Foreign holidays, recorded as at least one holiday each year in a sunny country over the last 10 years (scored yes/no). (iv) Cumulative sun exposure in years (weekdays and weekends considered separately in the three age categories above and combined). (v) The extent of occupation spent outdoors was expressed in units (proportion of time spent outdoors x10) with odds ratios relating to a 10% change in the proportion of outdoor working.

Genotype identification
PCR assays were used to identify the A->C change in exon 1 (codon 192) of TYR (19), the exon 2 (FokI) and exon 9 (TaqI) variants in VDR (20) and MC1R Val92Met, Asp294His and Asp84Glu (18) in DNA from peripheral blood. MC1R Arg151Cys and Arg160Trp were also detected using primers 5'-TCTCCATCTTCTACGCATTG-3' and 5'-GCCAGCATGTGGACGTACAG-3' to amplify a 202 bp product. PCR conditions were 95°C for 2 min, 35 cycles of 95°C for 1 min, 55°C for 1 min, 72°C for 1 min and 72°C for 3 min. Arg151Cys was identified by digestion with BsrDI (65°C, 18 h) and electrophoresis in 2% agarose (Arg151, 180 and 22 bp; Cys151, 202 bp). Arg160Trp was identified by digestion with SacII (37°C, 18 h) and electrophoresis in 3% agarose (Arg160, 156 and 46 bp; Trp160, 202 bp). In analysis of associations between MC1R genotypes and outcome, we compared frequencies of homozygotes for wild-type alleles against combined frequencies of heterozygotes and homozygotes for mutant alleles. This approach was used because mutant allele frequencies are generally uncommon and both heterozygotes and homozygotes are associated with sun-sensitive phenotypes (10).

Statistical analysis
Stata (version 6; Stata, College Station, TX, USA) was used for all analyses. We used logistic regression analysis to determine if the frequencies of individual factors were different between groups. In our main analyses we determined whether individual parameters of UV exposure, skin type or genotypes were associated with (i) bone metastases (presence versus absence), (ii) T stage (early, stages 1, 2 versus advanced, stages 3, 4) and (iii) tumour grade (low/moderate versus high grade). These stratifications were selected because they are used clinically in assessment of prognosis. These outcome measures are generally linked though they reflect different aspects of tumour biology and may be dependent on different genetic and environmental factors. Further, since time of disease onset cannot be known, patient age is a proxy for time since onset. Accordingly, all statistical models were corrected for age at diagnosis and the remaining two outcome parameters (e.g. age, stage and grade when examining associations with metastases). In secondary analyses, we used forward step-wise logistic regression (threshold for inclusion/exclusion of a variable; P = 0.10) to determine the most significant set of predictors. Associations between characteristics and metastases were studied in the 182 patients in whom radionuclide scintigraphy was available. We also performed the same analyses in the total group of 210 cases (data not shown). Inclusion of the 20 patients without scintigraphy results and no clinical evidence of metastases and 8 cases with evidence of metastases, resulted in the same significant variables being chosen with similar P values and odds ratios. We recognize that examining eight genotypes for links with phenotype risks identification of falsely significant associations because of the performance of many tests of significance. However, as correction for multiple testing increases risk of type II errors (21,22), we present uncorrected p values but recognize these exploratory findings require confirmation in another patient group.


    Results
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Associations between UV exposure, skin type, genotypes and metastatic state
UV exposure parameters and skin type data in 182 patients with and without bone metastases (identified using radionuclide scintigraphy) are shown in Table IGo. Advanced T stage (P < 0.001, OR 5.3, 95% CI 2.3–12.2) and high grade histology (P = 0.0021, OR 3.3, 95% CI 1.6–7.0) were significantly associated with metastases in a logistic regression model that also included age at diagnosis. These three parameters were included in subsequent models. Table IGo shows that none of the UV exposure parameters were associated with metastases. In contrast, patients with skin type 4 were at significantly increased risk of developing bone metastases compared with cases with skin type 1–3. Table IIGo shows genotype frequencies in patients with and without metastases. MC1R Val92/Val92 and VDR ff were associated with increased risk of metastases (ORs 4.30 and 4.98, respectively). TYR genotypes were not associated with metastases in models that included advanced stage and high grade histology (Table IIGo). Inspection of the data in Table IIGo, however, suggested that the A2 allele was associated with reduced risk of metastases; allele frequencies in cases with positive bone scans was 0.507 and in those with negative scans, 0.591. Indeed, when the analysis was repeated without advanced stage and high grade histology in the model, TYR A1A2 was associated with reduced risk (P = 0.033), though the association with TYR A2A2 failed to achieve significance (Table IIGo). Analysis of associations of UV exposure parameters, skin types and the other genotypes with metastases using logistic regression models that excluded advanced stage and high grade histology resulted in P values and ORs that were similar to those shown in Tables I and IIGoGo.


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Table I. Association of UV exposure and skin type with bone metastases in prostate cancer cases
 

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Table II. Association of genotypes with bone metastases in prostate cancer cases
 
To identify the most significant set of predictors of metastases, we used a step-wise routine that included the UV exposure parameters, age, skin type (type 4 versus 1–3), genotypes, high grade and advanced stage. Table IIIGo shows that advanced stage and high-grade disease were significantly associated with metastases. The significant associations between metastases and skin type 4, MC1R Val92/Val92 and VDR ff, observed when these factors were studied individually, were also found in the step-wise model. TYR genotypes were not significantly associated with metastases in this model.


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Table III. Step-wise analysis to identify predictors of metastasis in prostate cancer cases
 
Associations between UV exposure, skin type, genotypes and T stage
We classified patients into binary groups on the basis of early and advanced clinical T stage (94 and 116 patients, respectively). Metastases (P < 0.001, OR 5.2, 95% CI 2.24–12.1) and high grade histology (P = 0.006, OR 2.78, 95% CI 1.34–5.72) were significantly associated with advanced T stage in a logistic regression model that also included age at diagnosis. These parameters were included in subsequent models. We found that cumulative exposure (P = 0.005, OR 0.85/year, 95% CI 0.76–0.95) and increasing proportion of outdoor occupation (P = 0.001, OR 0.84/unit, 95% CI 0.76–0.93) were significantly associated with reduced risk of tumours with advanced T stage. We found no significant associations between skin type, MC1R, TYR or VDR genotypes and advanced clinical T stage (range of P values 0.17–0.98, range of ORs 0.49–2.24). In a logistic regression analysis in which metastases and high grade histology were excluded, the association between TYR A2A2 and advanced T stage approached significance (P = 0.052, OR 0.44, 95% CI 0.19–1.01). Analysis of associations of exposure parameters, skin types and the other genotypes with advanced stage using models that excluded metastases and high grade histology resulted in P values and ORs that were similar to those shown in Tables I and IIGoGo.

In a step-wise routine including UV parameters, age, presence of metastases, high-grade tumour, skin type (type 4 versus 1–3) and all genotypes, metastases (P < 0.001, OR 6.28, 95% CI 2.51–15.7), high-grade tumours (P = 0.001, OR 3.72, 95% CI 1.68–8.23) and outdoor occupation (P = 0.001, OR 0.84/unit, 95% CI 0.76–0.93) were significantly associated with advanced stage. The association of TYR A2A2 with advanced T stage approached significance (P = 0.089, OR 0.49, 95% CI 0.21–1.11).

Associations between UV exposure, skin type, genotypes and tumour grade
We classified patients into binary groups on the basis of well/moderately and poorly differentiated tumours (112 and 78 patients, respectively). Metastases (P = 0.002, OR 3.26, 95% CI 1.53–6.90) and advanced clinical T stage (P = 0.005, OR 2.81, 95% CI 1.37–5.79) were significantly associated with high grade histology and were included in subsequent models. Neither the parameters of UV exposure, skin type, MC1R, TYR nor VDR genotypes (range of P values 0.07–0.95, range of ORs 0.02–2.33) were significantly associated with high tumour grade. When the logistic regression analysis was repeated without advanced stage and metastases in the model, the association between TYR A2A2 and high-grade was significant (P = 0.040, OR 0.41, 95% CI 0.17–0.97). Analysis of associations of UV exposure parameters, skin types and the other genotypes with high grade histology using models that excluded advanced stage and metastases resulted in P values and ORs that were similar to those shown in Tables I and IIGoGo.

In a step-wise routine including UV parameters, age, presence of metastases, clinical stage, skin type (type 4 versus 1–3) and all genotypes, we found that only metastases (P = 0.002, OR 3.25, 95% CI 1.54–6.88), advanced stage (P = 0.005, OR 2.81, 95% CI 1.37–5.78) were associated with high-grade tumours.


    Discussion
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
It has been proposed that environmental influences on the progression of prostate cancer include duration or intensity of UV exposure (2,7), as well as contributions from diet and other factors. We have now examined, for the first time, the association between outcome and UV exposure and host characteristics linked with response to UV. We presumed that the putative effects of UV on outcome will be mediated by extent of exposure, interaction between UV and skin and by delivery of resulting chemicals to the prostate. Thus, genes involved in pigmentation response are candidates for outcome.

Linking outcome in prostate cancer with UV is difficult because assessment of lifetime exposure must consider intensity, duration and timing of exposure. Such data can only be collected retrospectively, usually many decades after exposure events. Several questionnaires have been designed to measure long-term UV exposure. We used a questionnaire, devised and validated in skin cancer studies (15,16), that assesses each of the different aspects of exposure.

We studied three outcome parameters. In general, aggressive, rapidly growing, large primary tumours are most likely to metastasize. However, there are frequent exceptions. Thus, small, well-differentiated tumours may metastasize while larger, rapidly growing lesions remain localized. These outcome parameters, therefore, reflect different aspects of tumour biology and may be dependent on different genetic and environmental effects. We recognize that the cross-sectional approach we have used may allow misclassification of patients. Thus, we presumed that all untreated patients will eventually develop metastases and accordingly, included age as a factor in our statistical models. Clearly, classification errors may have occurred if cases with micro-metastases were undetected and if other patients developed spread after recruitment. Similarly, clinical T stage may also be subject to classification errors. Histological grade is fixed at diagnosis and should not change. Importantly, as expected, the three parameters were significantly associated with each other in the statistical models.

We found that several parameters of UV exposure were associated with outcome in prostate cancer. Thus, both cumulative exposure and outdoor occupation were protective against tumours with an advanced T stage and patients with skin type 1 were at a significantly reduced risk (OR 0.17) of developing metastases than cases with skin type 4. Skin type classifies individuals by their ability to effect skin tanning and/or burning. This finding suggests that individuals who tan readily may demonstrate less systemic transmission of the effects of UV. We found no significant associations between metastases and the five parameters of UV exposure.

Multiple genes mediate pigmentation (8,10,11). We considered the influence of MC1R and TYR genotypes on outcome. The melanocyte stimulating hormone, acting through the MC1R, is a key regulator of human melanocyte proliferation and melanogenesis (11) and variants in MC1R have been associated with UV-sensitive phenotypes (8,10,11). Arg151Cys, Arg160Trp and Asp294His variants are associated with red/blonde hair and Asp84Glu is in linkage dysequilibrium with Asp294His. The Val92Met variant is not linked with red hair, though in some studies, but not others, has been associated with skin type (10,11,17). We studied the TYR allele resulting from an A->C change in exon 1. While this has not been shown to have functional consequences, the A1 and A2 alleles have similar frequencies and are useful markers. VDR is relevant as vitamin D is synthesized in skin following UV exposure and may act as a tumour inhibitor, retarding the progression of sub-clinical tumours. Further, vitamin D metabolites are internalized by melanocytes and effect TYR activity. Polymorphism at the VDR FokI restriction site alters the upstream ATG start codon resulting in the production of a shortened protein. The net effect of VDR ff compared with VDR FF, can be envisaged as a reduction in the cellular effect of 1,25(OH)2 vitamin D (12). The TaqI site also appears to have functional consequences, though we did not find a link between metastases and this polymorphism. Interestingly, associations between VDR tt and VDR ff and outcome (Breslow thickness >= 1.5 mm) have been found in malignant melanoma (20).

MC1R Val92/Val92 (OR 4.30) and VDR ff (OR 4.98) were associated with increased risk of metastases in logistic regression models that included advanced T stage and high grade histology. A step-wise routine showed that advanced stage disease (OR 8.9), MC1R Val92/Val92 (OR 5.8), high-grade (OR 4.2), skin type 4 (OR 3.8) and VDR ff (OR 3.8) were the most significant set of predictors of metastases in a model that included all variables. Neither MC1R Val92/Val92 nor VDR ff were associated with T stage or grade. The mechanism for these findings is unknown. In particular, it is unclear why MC1R Val92/Val92, but not other MC1R genotypes, is associated with metastases. The functional significance of this variant is unclear though it may result in increased synthesis of pheomelanin (8,10). We previously reported no associations between this genotype and susceptibility and outcome in malignant melanoma (18). The TYR A2 allele was associated with each of the three outcome markers in models that included only age suggesting it is association with an aspect of carcinogenesis common to all three outcome parameters.

In prostate cancer, UV exposure may explain why subclinical rather than malignant disease is very common in older men. Thus, autopsy prevalence of prostatic adenocarcinoma reaches 30% during the seventh decade of life (23). Hanchette and Schwartz (2) suggested that blood-borne factors, whose concentration is determined by UV, could ensure that tumours remain latent rather than progress to malignancy. This concept is compatible with studies showing effects of 1,25 (OH)2 vitamin D on tumour cell proliferation, differentiation and spread (7,12) and our findings that VDR variants are linked with bone metastases. We recognize that while UV appears critical in the development of skin cancers, its role in determining outcome in prostate cancer is speculative (7). Nonetheless, while our data are preliminary and require confirmation in a separate case group, they demonstrate consistency. Thus, aspects of UV exposure were associated with each of the outcome parameters. The link with TYR was also observed with each parameter. We believe, therefore, that these initial findings are compatible with studies indicating a protective effect for UV in several internal cancers including colon, breast, ovarian and prostate. The mechanism for this link may be through vitamin D and parathyroid hormone (7,24).


    Notes
 
3 To whom correspondence should be addressedEmail: paa00{at}keele.ac.uk Back


    Acknowledgments
 
We thank the staff of Wedgewood for their generous support.


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 

  1. Blair,A. and Fraumeni,J.F. (1978) Geographic patterns of prostate cancer in the United States. J. Natl Cancer Inst., 61, 1379–1384.[Medline]
  2. Hanchette,C.L. and Schwartz,G.G. (1992) Geographic patterns of prostate cancer mortality. Evidence for a protective effect of ultraviolet radiation. Cancer, 70, 2861–2869.[Medline]
  3. Ekman,P., Pan,Y., Li,C. and Dich,J. (1997) Environmental and genetic factors: a possible link with prostate cancer. Br. J. Urol., 79(suppl. 2), 35–41.[Medline]
  4. Powell,I.J., Banerjee,M., Sakr,W., Grignon,D., Wood,D.P., Novallo,M. and Pontes,E. (1999) Should African–American men be tested for prostate carcinoma at an earlier age than white men? Cancer, 85, 472–477.[Medline]
  5. Shröder,F.H. (1998) Endocrine treatment of prostate cancer. In Walsh,P.C., Retik,A.B., Vaughan,E.D. and Vine,A.J. (eds), Campbell's Urology. W.B.Saunders, Philadelphia, pp. 2427–2644.
  6. Lichtenstein,P., Holm,N.V., Verkasalo,P.K., Iliadou,A., Kaprio,J., Koskenvuo,M., Pukkala,E., Skytthe,A. and Hemminki,K. (2000) Environmental and heritable factors in the causation of cancer. New Engl. J. Med., 343, 78–85.[Abstract/Full Text]
  7. Studzinski,G.P. and Moore,D.C. (1995) Sunlight—Can it prevent as well as cause cancer? Cancer Res., 55, 4014–4022.[Abstract]
  8. Sturm,R.A., Box,N.F. and Ramsay,M. (1998) Human pigmentation genetics: the difference is only skin deep. Bioessays, 20, 1–11.[Medline]
  9. Oetting,W.S. and King,R.A. (1999) Molecular basis of albinism: Mutations and polymorphisms of pigmentation genes associated with albinism. Human Mutat., 13, 99–115.[Medline]
  10. Valverde,P., Healy,E., Jackson,I., Rees,J.L. and Thody,A.J. (1995) Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans. Nature Genet., 11, 328–330.[Medline]
  11. Abel-Malek,Z., Suzuki,I., Tada,A., Im,S. and Akcali,C. (1999) The melanocortin-1 receptor and human pigmentation. Ann. N. Y. Acad. Sci., 885, 117–133.[Medline]
  12. Haussler,M.R., Whitfield,G.K., Haussler,C.A., Hsieh,J.C., Thompson,P.D., Selznick,S.H., Dominguez,C.E. and Jurutka,P.W. (1998) The nuclear vitamin D receptor: biological and molecular regulatory properties revealed. J. Bone Miner. Res., 13, 325–349.[Medline]
  13. Taylor,J.A., Hirvonen,A., Watson,M., Pittman,G., Mohler,J.L. and Bell,D.A. (1996) Association of prostate cancer with vitamin D receptor gene polymorphism. Cancer Res., 56, 4108–4110.[Abstract]
  14. Ingles,S.A., Ross,R.K., Yu,M.C., Irvine,R.A., La Pera,G., Haile,R.W. and Coetzee,G.A. (1997) Association of prostate cancer risk with genetic polymorphisms in vitamin D receptor and androgen receptor. J. Natl Cancer Inst., 89, 166–170.[Abstract]
  15. Harvey,I., Frankel,S., Marks,R., Shalom,D. and Nolan-Farell,M. (1996) Non-melanoma skin cancer and solar keratoses. 1. Methods and descriptive results of the South Wales skin cancer study. Br. J. Cancer, 74, 1302–1307.[Medline]
  16. Ramsay,H.M., Fryer,A.A., Reece,S., Smith,A.G. and Harden,P.N. (2000) Clinical Risk Factors Associated with Non-melanoma Skin Cancer in Renal Transplant Recipients. Am. J. Kidney Dis., 36, 167–176.[Abstract/Full Text]
  17. Montironi,R. (2001) Prognostic factors in prostate cancer. Pathologists glean a wealth of clinical detail from the smallest piece of tissue. Br. Med. J., 7283, 378–379.
  18. Strange,R.C., Ellison,T., Ichii-Jones,F. et al. (1999) Cytochrome P450 CYP2D6 genotypes: associations with hair colour, Breslow thickness and melanocyte stimulating hormone receptor alleles in patients with malignant melanoma. Pharmacogenetics, 9, 269–276.[Medline]
  19. Giebel,L.B. and Spritz,R.A. (1990) RFLP for Mbo1 in the human tyrosine (TYR) gene detected by PCR. Nucleic Acid Res., 18, 3103.
  20. Hutchinson,P.E., Osborne,J.F., Lear,J.T., Smith,A.G., Bowers,B., Morris,P.N., Jones,P.W., York,C., Strange,R.C. and Fryer,A.A. (2000) Vitamin D receptor polymorphisms are associated with altered prognosis in patients with malignant melanoma. Clin. Cancer Res., 6, 498–504.[Abstract/Full Text]
  21. Cuzick,J. (1999) Interaction, subgroup analysis and sample size. In Boffetta,P., Caporaso,N., Cuzick,J., Lang,M. and Vineis,P. (eds), Metabolic Polymorphisms and Cancer. IARC Scientific Publications, no. 148 IARC, Lyon, pp. 109–21.
  22. Rosenberger,W.F. (1996) Dealing with multiplicities in pharmacoepidemiologic studies. Pharmacoepidem. Drug Safety, 5, 95–100.
  23. Scardino,P.T. (1989) Early detection of prostate cancer. Urol. Clin. North Am., 16, 635–655.[Medline]
  24. McCarty,M.F. (2000) Parathyroid hormone may be a cancer promoter—an explanation for the decrease in cancer risk associated with ultraviolet light, calcium and vitamin D. Med. Hypotheses, 54, 475–482.[Medline]
Received April 2, 2001; revised June 15, 2001; accepted June 18, 2001.