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.