1 Servicio de Oncología Médica, Hospital General Universitario de Alicante, Alicante; 2 Servicio de Oncología Médica, Hospital Clínico Universitario San Carlos, Madrid; 3 Servicio de Oncología Médica, Fundación Hospital de Alcorcón, Alcorcón, Madrid; 4 Servicio de Oncología Médica, Hospital Germans Trias I Pujol, Badalona, Barcelona; 5 Servicio de Oncología Médica, Hospital Universitari Sant Joan de Reus, Reus, Tarragona; 6 Servicio de Oncología Médica, Hospital Universitari Arnau de Vilanova, Lleida; 7 Servicio de Oncología Médica, Hospital General Universitario de Valencia, Valencia; 8 Servicio de Oncología Médica, Hospital Provincial de Castellón, Castellón; 9 Servicio de Oncología Médica, Hospital General Universitario de Elche, Elche, Alicante; 10 Servicio de Oncología Médica, Hospital Universitario Marqués de Valdecilla, Santander; 11 Servicio de Oncología Médica, Hospital Universitario Reina Sofía, Córdoba; 12 Servicio de Oncología Médica, Hospital Clínico Universitario Lozano Blesa, Zaragoza; 13 Servicio de Oncología Médica, Hospital Nuestra Señora de Aránzazu, San Sebastián; 14 Servicio de Oncología Médica, Hospital Clínico Universitario Virgen de la Victoria, Málaga; 15 Servicio de Oncología Médica, Consorci Sanitari de Terrassa, Terrassa, Barcelona; 16 Servicio de Oncología Médica, Hospital Virgen de los Lirios, Alcoy, Alicante; 17 Servicio de Oncología Médica, Hospital Universitario de Canarias, La Laguna, Santa Cruz de Tenerife; 18 Instituto de Oncología Corachán, Barcelona; 19 Servicio de Oncología Médica, Hospital de La Princesa, Madrid; 20 Department of Biostatistics, Pharmacia S.A., Barcelona, Spain
Received 10 April 2003; revised 12 August 2003; accepted 28 August 2003
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ABSTRACT |
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A prospective randomized clinical trial was implemented to assess whether the concomitant or the sequential addition of tamoxifen to chemotherapy provides improved clinical benefit in the adjuvant treatment of breast cancer in postmenopausal patients.
Patients and methods:
Four-hundred and eighty-five patients with node-positive operable disease were randomized to receive tamoxifen (20 mg/day) concomitantly (CON) or sequentially (SEQ) to EC chemotherapy (epirubicin 75 mg/m2 + cyclophosphamide 600 mg/m2 on day 1, every 21 days for four cycles).
Results:
In the 474 fully evaluable patients there were 96 events; eight being second neoplasms and 88 being related to the breast cancer. Of these, 48 of 88 occurred in the CON arm and 40 of 88 in the SEQ arm. The KaplanMeier estimation of disease-free survival (DFS) at 5 years was 70% in the CON and 75% in the SEQ group (log-rank test, P = 0.43). Adjusted hazard ratio for treatment was 1.11 (95% confidence interval 0.711.73; P = 0.64).
Conclusion:
This study fails to show an advantage of one treatment arm over the other, but a trend, albeit non-significant, appears to favor the sequential addition of tamoxifen to epirubicin + cyclophosphamide and, as such, warrants further investigation.
Key words: adjuvant chemotherapy, adjuvant tamoxifen, breast cancer, concomitant, cyclophosphamide, epirubicin, sequential
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Introduction |
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Basic research on the interaction between TAM and chemotherapy has been conducted in different laboratories and the findings yielded some insight with respect to the complexity of this issue. Interactions that were different from straightforward cytokinetic effects were reported and included several biochemical, pharmacological and biological interactions with different chemotherapy agents. Conflicting observations with respect to the most commonly used chemotherapy drugs undermined the credibility of the clinical relevance of the findings. For example, melphalan showed uniform antagonism [4, 5] and, while a synergism between 5-fluorouracil and TAM was reported by one group [4], the contrary was observed in other laboratories [57]. Similar contradictory results were published with doxorubicin, which was shown to be additive [5] or antagonic [7, 8] in different laboratories. Given the heterogeneity in the spectrum of interactions between TAM and chemotherapeutic agents, the net effect on the patient could be quite unpredictable.
The existing clinical experience with metastatic breast cancer has been of limited help on this issue. Although response rates improved slightly there were no demonstrable survival benefits in favor of combined chemo-endocrine therapy in a randomized clinical trial [9]. Interpreting these findings was challenging because they were consistent with not only a lack of interaction between TAM and chemotherapy but also with a less than additive interaction [10]. The existing contemporary experience regarding the adjuvant setting was summarized in the 1992 version of the meta-analysis conducted by the EBCTCG [11]. The conclusions with regard to postmenopausal women were that the risk of disease recurrence was lower when combining TAM with the chemotherapy than with any of the therapies used alone. These conclusions were translated into recommendations for clinical practice by the panel of Sant Gallen International Conference [12] but "the proper sequencing of chemotherapy and tamoxifen remains to be defined". This 1992 meta-analysis was based, largely, on the NSABP B-16 results, a trial which used TAM and chemotherapy simultaneously and from which the authors interpreted their positive results as a demonstration of an absence of unfavorable interaction between TAM and the different chemotherapy regimens used in the trial. As a logical conclusion the authors stated: "...until studies prove that delaying the administration of TAM until completion of chemotherapy results in a greater benefit, administering the two modalities simultaneously is an appropriate treatment strategy".
In order to clarify the doubts regarding the sequence of chemotherapy and TAM administration in the adjuvant therapy of breast cancer, we decided to implement a prospective randomized clinical trial.
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Patients and methods |
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Randomization, stratification and treatment
The trial was designed to answer a single question, i.e. whether administration of TAM concurrently (CON) or sequentially (SEQ) to scheduled chemotherapy could offer clinical benefit to the breast cancer patient. The only difference between the two treatment arms was the starting point of TAM administration. A central randomization procedure was performed with stratification by center and surgical procedure (lumpectomy or mastectomy). Allocation to CON or SEQ was carried out in blocks of eight patients, established according to a table of random numbers. Patient number and treatment group assignment was communicated to the investigator on request by telephone call and confirmed by fax. Patients were to receive epirubicin (75 mg/m2) plus cyclophosphamide (600 mg/m2) intravenously every 21 days, for four cycles. We deliberately chose an equivalent regimen to that of the NSABP AC trial but with fewer risks of cardiotoxicity. We estimated the epirubicin dose of 75 mg/m2 as being equivalent to 60 mg/m2 of doxorubicin, based on published data [13, 14]. All patients were to receive TAM 20 mg daily by mouth for 5 years. Patients randomized to the CON arm were to take their first dose on day 1 of the first cycle of chemotherapy while the patients randomized to the SEQ arm commenced TAM on day 21 after the fourth cycle.
Study objectives and statistical considerations
Statistical estimation of the number of patients needed presented some challenges. There were no clinical antecedents to provide an indication regarding the size of the difference nor the direction of benefit to be expected. Pre-clinical data were contradictory with respect to doxorubicin and TAM interactions, so neither synergism nor antagonism could be factored into the calculations. As already stated, the success of concurrent administration of anthracycline + TAM was somewhat ambiguous since the combination was considered better than TAM alone, but the results did not exclude the possibility of an even better outcome in the case of there being an antagonistic effect between anthracycline and TAM. Hence we chose a bilateral test so as not to pre-judge the direction of treatment advantage. Due to the unavoidably arbitrary nature of the choice and taking into account feasibility considerations, we opted for a 10% difference in 5-year disease-free survival (DFS) between treatment arms while acknowledging that even 1% difference would be clinically relevant. The primary goal was 5-year DFS and, for the purposes of the statistical analyses, an event was defined as the first documented evidence of local, regional or distant recurrence, recurrence of tumor in the ipsi-lateral breast following lumpectomy, second primary cancer, or death without recurrence of cancer. In consideration of the meta-analysis data, we set the expected 5-year DFS at 50%. The statistical significance of the difference between DFS distributions by treatment was determined by log-rank test [15]. For an risk of 5%, a power of 80%, a proportion of events in the control arm of 0.5, and a difference in the proportion of events between the two arms of 0.1, and a two-sided test of probability, the number of patients needed was estimated as 362 per treatment arm [16].
A multiple proportional Cox model was performed to test the value of the treatment while adjusting for the main prognostic factors.
The proposed recruitment period was 3 years, and an interim analysis was planned for 2 years later. The trial was opened to recruitment in June 1995. Recruitment was running slower than planned and by the third year the required number of patients was not reached. The Steering Committee of GEICAM decided to prolong the recruitment period for two more years. By July 2000 the problem of recruitment persisted and the Steering Committee opted to close the enrolment.
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Results |
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Discussion |
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The findings from an equivalent trial (INT-0100) by Albain et al. [20] are controversial as well. Compared to the under-powered GEICAM trial, the INT is extensive and with protracted follow-up but the statistical aspect of the INT may be considered equivocal. This is because one-sided tests of significance were used despite the direction of the outcomes not being known and in which the two-sided tests are more appropriate. Further, the 95% CI of the adjusted hazard ratio included the unit 1. It may be argued that INT-0100 results constitute level I evidence and that they may be sufficient to warrant a change in clinical guidelines. In this setting, GEICAM-9401 results take on considerable importance because they confirm and extend the INT conclusions. Of considerable note is that the findings are consistent between both trials, i.e. the SEQ treatment scheme shows consistently better results than the CON scheme. The observations of DFS curves that are identical over the first 3 years but diverge subsequently to show an absolute difference of 5% at 5 years, of adjusted hazard ratios of 11% in GEICAM and 18% in INT are remarkable for their similarity in the two trials despite the differences in the chemotherapy regimens employed (epirubicincyclophosphamide in the GEICAM trial and CAF in the INT). Pooling the present data with that from the INT would probably improve the overall statistical significance and would strengthen the main conclusion which would be that of SEQ superiority. The credibility of these results is important for clinical practice and, should the recommendation be accepted in the oncology community, sequential administration should become the standard of care. For those clinical practitioners who may be concerned that TAM could lose part of its efficacy as a consequence of delaying its administration, the results from the French trial TAM-2 [21] provide reassurance with the demonstration that, even when administered after considerable delay in adjuvant therapy, TAM delivers a degree of clinical benefit.
From a perspective of the current study, the decision to include patients whose tumors were hormone receptor negative could be seen as inappropriate. It was a debatable, but conservative, decision at the time of the study design and was based on the published literature. The 1992 EBCTCG meta-analysis suggested a small but worthwhile benefit of TAM administration in hormone receptor negative patients. Moreover, the reduced cancer risk for the contralateral breast together with the reported benefits on skeleton (and possibly on cardiovascular risk) were considered as additional reasons to administer TAM to hormone receptor negative patients. It was in the 1998 update of the EBCTCG meta-analysis [22] that the futility of prescribing TAM for patients with hormone receptor negative tumors was stated. Whether the antagonism between TAM and anthracycline-containing regimens can be applied to cyclophosphamide, methotrexate and fluorouracil (CMF) regimens remains to be clarified. When designing our trial we chose an anthracycline-containing chemotherapy regimen because there were some theoretical reasons to expect synergism of action [5]. There were no equivalent considerations in support of CMF. The evidence supporting the value of adding CMF to TAM in postmenopausal patients with estrogen receptor positive tumors [12] was scarce at the time the present trial was inaugurated. A further consideration behind our choice of an anthracycline-containing chemotherapy was the reported incidence of thromboembolisms. The ECOG study [17] in postmenopausal women reported an incidence of venous events of 0.4%, 2.3% and 3.59.1% for observation alone, TAM, and combined TAMchemotherapy groups, respectively. The corresponding values for arterial events were 1.7%, 1.2% and 01%, respectively. In contrast to these findings, the NSABP TAM + AC trial [23] reported an incidence of 2.3% for DVT and 0.8% for PE. These values were not very different from the observed incidence with TAM alone in the same trial, i.e. 0.8% and 0.8% for DVT and PE, respectively [23]. The CanadianNCI trial [18] reported an incidence of thromboembolic events of 13.6% in the CMF + TAM combination compared to 2.6% for the TAM treatment arm alone. Our observation of an incidence of DVT + PE of 11 of 474 patients (2.32%) is closer to the NSABP TAM + AC trial than to the other reported studies. The incidence of stroke/CVA was four of 474 patients (0.84%) which was higher than the 0.22% expected incidence for TAM in healthy women aged >50 years [24], but well within the expected limits for postmenopausal breast cancer patients [17].
One of the most intriguing issues arising out of this trial is the biological mechanism underlying the observed results. The antagonism observed between TAM and chemotherapy is a clinical reality but the biological inter-relationship is far from clear. Certainly, those hypotheses predicting an additive or synergistic effect such as reversal of p170-mediated resistance to anthracyclines by TAM [25, 26], or calmodulin inhibition [27] can be rejected since they appear not to play a clinically relevant role, at least at the drug dose used in the present trial. Cytokinetic resistance to chemotherapy that may be induced by TAM could be the most plausible explanation for the observed results. TAM appears to modify the cell cycle transit and reduces the number of proliferating cells [28] and, thus, creates a cytokinetic resistance to chemotherapy [1, 5]. Consistent with this interpretation is the pattern of the DFS curves in which no interaction is apparent during the first 3-year period, i.e. patients with the quickest relapse are, probably, TAM-resistant. However, the antagonism becomes apparent in patients with late relapse and represents, probably, patients who have TAM-sensitive tumors. Also, the slow-growing micro-metastases with stronger dependence on estrogens to maintain the pace of proliferation are, probably, more sensitive to the antiproliferation effect of TAM. Although it has been a well-documented laboratory phenomenon, our trial, together with the INT, is the first clinical evidence supporting this hypothesis in the adjuvant setting. The antagonism that a cytostatic agent such as TAM could exert on cytotoxic drugs should alert the clinical research community regarding the possibility of this interaction being a more general phenomenon. In the present era of new targeted drug development, some of them may work as cytostatic agents and, as such, the opportunity to use them in SEQ or CON schemes with chemotherapy should not be missed.
The cytokinetic hypothesis is not the only possible interpretation of the observed antagonism. Tamoxifen has other effects such as anti-angiogenic, cell-membrane perturbation of structure and function, as well as interaction with growth factors and signaling molecules [29]. Whether any of these pathways plays a role remains speculative.
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Acknowledgements |
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FOOTNOTES |
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