Tamoxifen and oophorectomy in the treatment of recurrent breast cancer: a Southwest Oncology Group Study.

The relatively short survival following chemotherapy in patients with metastatic carcinoma of the breast and the introduction of antiestrogens has led to renewed interest in the hormonal therapy of breast cancer. Pritchard et al. (Cancer Treat. Rep., 64: 787-796, 1980) have recently stated that response to the antiestrogen tamoxifen (TAM) strongly predicts a subsequent response to oophorectomy in premenopausal patients. The Southwest Oncology Group administered TAM to pre- and postmenopausal women with first recurrence of breast cancer. Following response and subsequent relapse, or after no response, patients underwent an oophorectomy while continuing on TAM. None of 14 premenopausal patients who responded to TAM had a response to oophorectomy plus TAM, while 5 of 22 had a remission with oophorectomy plus TAM after initially failing with TAM alone. The reverse was seen in postmenopausal women; 4 of 18 responders to TAM subsequently responded to oophorectomy plus TAM, but none of 18 TAM failures responded to oophorectomy plus TAM. These results suggest that in the premenopausal women the TAM dose may be insufficient to block all estrogen action and that oophorectomy, by removing the major source of estrogen, can result in a more effective antiestrogen action of TAM leading to a response. No explanation is readily available for the results in postmenopausal patients.