Estrogen priming before progestin therapy in advanced breast cancer

We conducted a prospective trial of sequential administration of oral ethinyl estradiol (EE) with medroxyprogesterone acetate (MPA) in postmenopausal women with estrogen receptorpositive breast carcinoma that had not been treated with additive hormonal therapy. A 14-day treatment cycle consisted of 1.0 mg/day EE on days 1 and 2, 400 mg/day MPA on days 3 through 12, and no treatment on days 13 and 14. Seven (44%) of the 16 evaluable patients had partial responses, but no complete responses were observed. The median duration of response was 7.6 months. Fifty-three percent of the patients experienced therapy-related complications including two cases of thromboembolism. Estrogen priming before progestin therapy as used in this study cannot be recommended for routine use because the response rate does not seem to be better than that of monohormonal therapy in the face of a high incidence of complications.