Tamoxifen versus ethinyl estradiol in the treatment of postmenopausal women with advanced breast cancer.

In a randomized study, 63 postmenopausal patients with advanced breast cancer were treated with ethinyl estradiol (EE2) or the antiestrogen tamoxifen to compare the efficacy and side effects of both drugs. EE2 was always given in combination with chlorothiazide to prevent fluid retention. Pretreatment characteristics of the patients of both groups did not differ significantly. Objective remissions were achieved in 31% of the EE2-treated patients and in 33% of the tamoxifen-treated patients. The median duration of remission was 12 months (range, 5-32) for the EE2 group and 11 months (range, 5-26) for the tamoxifen group (P greater than 0.1), and the estimated median survival times from the start of treatment were 31 and 25 months, respectively (P greater than 0.1). The best treatment results in both groups were obtained in patients with estradiol receptor-positive tumors and less advanced disease. After therapy was stopped, objective withdrawal responses were observed in EE2- but not in tamoxifen-treated patients. Two patients receiving EE2 had to discontinue treatment because of drug-related liver function impairment. Both patients had cholelithiasis. Two patients in the tamoxifen-treated group discontinued therapy because of nausea. Deep venous thrombosis occurred in one patient receiving EE2, whereas two patients receiving tamoxifen developed superficial thrombophlebitis. Other side effects in both groups of patients, including initial hypercalcemia, were mild. It is concluded that both treatment regimens, EE2 or tamoxifen, are equally effective with respect to induction and duration of remission in postmenopausal patients with advanced breast cancer. Side effects of EE2 therapy appeared to be more serious than those of tamoxifen treatment.