Thirty-nine evaluable, postmenopausal patients with metastatic breast carcinoma were treated with medroxyprogesterone acetate administered orally at daily doses of 800 mg/day in 29 patients and 400 mg/day in 10 patients. One patient experienced a complete remission and 16 had partial remissions for an objective remission rate of 44%. There was no apparent difference in response between the two dose levels. Median remission duration was 8 months, and median survival for the whole group is expected to exceed 18 months. Increased appetite (66%) and weight gain (97%) were the most common side effects, followed by fluid retention, muscle cramps, and increased blood pressure. Performance status improved and white blood cell and platelet counts increased in the majority of patients. Medroxyprogesterone acetate is an effective hormonal agent in the treatment of metastatic breast cancer.

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A clinical trial of sequential tamoxifen and medroxyprogesterone acetate (MPA) was carried out in 36 women with metastatic breast cancer in order to evaluate the therapeutic efficacy of this regimen and to determine if tamoxifen would increase progesterone receptor (PR) levels and thereby increase response to MPA. Fourteen patients (39%) responded to this treatment, with the duration of remission ranging from 2 to 24 + months (the mean and median were 11 months). In 22 patients, PR levels were measured both before and after 7 days of tamoxifen administration. In PR-positive patients, PR changes induced by tamoxifen did not appear to increase the response rate. In PR-negative patients, PR became positive in 3 patients following tamoxifen treatment, with 2 of 3 responding to treatment, whereas in 11 others whose PR levels remained negative, only one response was observed. Our results suggest that potentiation by tamoxifen was not observed, since in our previous study, MPA alone was equally effective. Thus, tamoxifen and MPA should be given independently for palliation of metastatic breast cancer, and MPA should be administered following therapy with tamoxifen.

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