Phase II study of tamoxifen: report of 74 patients with stage IV breast cancer.

: Tamoxifen (NSC-180973), a synthetic antiestrogen, was studied for efficacy and toxicity in patients with metastatic breast adenocarcinoma. Two dose levels were used, 10 mg bid and 15 mg/m2 bid, in separate groups. In the 10-mg bid dosage group, 30 of the 31 patients were considered evaluable for efficacy. Five complete and 11 partial responses were recorded, for an overall response rate of 53%. In the 15-mg/m2 bid dosage group, 44 of the 45 patients were considered evaluable for efficacy. Three complete and 16 partial responses were recorded, for an overall response rate of 43%. All 76 patients were evaluated for toxicity. Side effects were generally mild, consisting mostly of hot flushes, transient leukopenia, transient thrombocytopenia, nausea, and fluid retention. A high degree of correlation between response and positive estrogen-receptor assay suggests the value of the test as a means to select patients for tamoxifen treatment. The conclusion from this study is that tamoxifen used as a single agent is an effective drug with minimal toxicity for treatment of metastatic breast adenocarcinoma.