Adjuvant CMFP versus CMFP plus tamoxifen versus observation alone in postmenopausal, node-positive breast cancer patients: three-year results of an Eastern Cooperative Oncology Group study.

After mastectomy, 265 postmenopausal patients with node-positive breast cancer were stratified according to pathologic nodal status and estrogen-receptor (ER) status and randomized to receive either 12 cycles of cyclophosphamide, methotrexate, 5-fluorouracil, and prednisone (CMFP), or CMFP plus tamoxifen (CMFPT), or observation alone. Patients entered the study between March 1978 and July 1981. Cox regression analysis indicated that, compared to observation alone, chemotherapy (CMFP and CMFPT groups combined) led to a significant reduction in relapses by the end of the first year of study in every examined prognostic subgroup. However, after the first year the relapse-free survival curves of all treatment groups tended to merge, so that by three years 52% of the observation group and 51% of the chemotherapy groups remained disease free. Chemotherapy continued to show a significantly superior relapse-free survival rate for three years only in the subgroup of patients with ER-negative tumors (the subgroup with the largest relapse-free survival advantage at one year). The addition of tamoxifen produced no benefit or harm in any prognostic subcategory examined. ER status was prognostically important for predicting early relapse only in those patients not receiving chemotherapy, due to the greater effectiveness of this chemotherapy to prevent early relapse in the ER-negative subgroup. Treatment has had no early effect on survival. As breast cancer continues to recur even after ten or more years, later relapse patterns may alter these results.