Progesterone receptor level as a predictor of response to megestrol acetate in advanced breast cancer: a retrospective study.

Megestrol acetate (160 mg/day) produced a response rate of 44% in a retrospective series of 39 evaluable patients with advanced breast cancer. The estrogen-receptor (ER) level was greater than 10 fmols/mg of protein in 28 patients, and the progesterone-receptor (PR) level was greater than 10 fmols/mg of protein in 26 patients. ER and PR levels, age, and disease-free interval were analyzed for their relationship to response. The PR was the single best predictor of response to megestrol acetate; the addition of ER added 2% to the predictive accuracy rate of PR alone.