A phase I/II study of high-dose megestrol acetate in the treatment of metastatic breast cancer

A dose-response relationship has been suggested for medroxyprogesterone acetate in the treatment of advanced breast cancer. To determine the tolerability and efficacy of increasing doses of megestrol acetate in the treatment of metastatic breast cancer, we conducted a phase I/II study among 57 patients. Three patients each received 480,800, and 1280 mg/d; 48 patients received 1600 mg/d. Of the 57 patients, 56 patients had had disease progression on prior hormone therapy, chemotherapy, or both. Twenty-seven patients had previously received standard-dose MA (160 mg/d). Among the 37 patients with measurable disease, high-dose megestrol acetate (HDMA) produced 6 (16%) complete responses (CRs) and 6 (16%) partial responses (PRs); 11 patients achieved stable disease (SD). HDMA resulted in improvement or stabilization in 12 of the 20 patients with evaluable, non-measurable disease. There were no responses among the 6 patients with liver metastases. Among the 27 patients who were previously treated with standard-dose MA, including 9 patients with primary treatment failure, HDMA resulted in 1 CR, 3 PRs, and 10 SD. Toxicities, which were mild and reversible, included fluid retention, hypertension, hyperglycemia, and mild congestive heart failure. Two patients had superficial phlebitis. The most profound side effect was weight gain which occurred in 43 patients (75%). This study suggests a dose-response relationship for MA in the treatment of advanced breast cancer. A randomized trial to determine the optimal dose is ongoing.