Evidence of a castration-mediated effect of adjuvant cytotoxic chemotherapy in premenopausal breast cancer.

Abstract

This prospective randomized trial, conducted by the Danish Breast Cancer Cooperative Group, is the largest study, so far, of adjuvant chemotherapy in premenopausal breast cancer. The trial is unique in that it is nationwide and based on a nonselected population of patients, and is the only adjuvant trial studying the effect of cyclophosphamide monotherapy. After total mastectomy with axillary node sampling, followed by local radiotherapy, 1,032 pre- and perimenopausal women with operable breast cancer were randomized to observation alone, or to adjuvant chemotherapy for 1 year with either cyclophosphamide monotherapy or with a combination of cyclophosphamide, methotrexate, and 5-fluorouracil (CMF). As of January 1987, median follow-up was 68 months. From early on both cyclophosphamide alone and CMF were found to improve recurrence-free survival (RFS) significantly and to a similar degree (P = .0001). However, an overall survival advantage did not become evident until 5 years after the start of treatment. So far, this advantage appears to be more pronounced in CMF (P = .0065) than in cyclophosphamide-only patients (P = .08). Thus, the study confirms the findings of the National Surgical Adjuvant Breast Project (NSABP) and Milan trials that adjuvant chemotherapy prolongs the survival of premenopausal women with early breast cancer. A retrospective analysis revealed that, in contrast with CMF, cyclophosphamide alone did not improve RFS significantly in subsets of patients without amenorrhea, with estrogen-receptor (ER) negative tumors, and with tumors of low histological differentiation. Assuming that cyclophosphamide alone is a less tumoricidal treatment than CMF, these findings suggest that the effect of adjuvant cytotoxic chemotherapy is mediated partly through chemical castration, and partly through a purely cytotoxic effect.