- Tamoxifen was evaluated as initial hormone therapy for metastatic breast cancer in 85 premenopausal patients. Tamoxifen responders continued on tamoxifen, while tamoxifen failures and initial responders who later progressed were to receive ovarian ablation next. Of 74 evaluable patients, 5 had complete responses (CR) and 15 had partial responses (PR) while 12 remained stable (ST), giving response rates of 27% (CR + PR) or 43% (CR + PR + ST). Of the 23 patients who initially responded (CR + PR + ST) to tamoxifen but then progressed and received ovarian ablation alone, 15 are assessable. Nine (60%) responded (CR + PR + ST) to ovarian ablation. Sixteen patients who failed tamoxifen had ovarian ablation alone, and of 14 assessable patients 2 had ST while 12 progressed. Thus response to tamoxifen strongly predicted response to ovarian ablation (P = 0.021). Serial follicle stimulating hormone, prolactin, and estradiol levels suggested that tamoxifen does not act by induction of a "medical ovariectomy" or by alteration of prolactin levels in premenopausal patients.