The efficacy of adjuvant treatment with tamoxifen was evaluated in protocol DBCG 77 C. Postmenopausal high risk patients (tumor greater than 5 cm, positive axillary nodes, or invasion to skin/fascia) were randomized after total mastectomy and axillary sampling to postoperative radiotherapy (control) or to radiotherapy plus treatment with tamoxifen (TAM), 30 mg daily for 1 year. A total of 1,716 patients entered the study. At 8 years of follow-up, (7 years median time of observation), we observed a significant increase of recurrence-free survival for the TAM treated group and a reduction in mortality, which is significant for patients less than 70 years of age. Retrospectively, an increased recurrence-free survival in TAM treated patients was significant in the following subgroups: tumor less than 5 cm, positive lymph nodes, anaplasia grade II and estrogen receptor level greater than 100 fmol/mg cytosol protein. In the subsequent trial (DBCG 82 C), 1,347 postmenopausal patients less than 70 years were randomized to one of the following 3 regimens: radiotherapy + tamoxifen, 30 mg daily for 1 year (TAM), TAM alone, or TAM + CMF (CMF i.v. day 1 every 4 weeks x 9). The survival is similar in the 3 groups at 4 years (2 years median time of observation).