Oral gestrinone: a novel antiprogestin with no antitumor activity in endocrine-sensitive breast cancer.

We have treated 15 patients with locally advanced or metastatic breast cancer using the synthetic 19-norsteroid gestrinone (2.5 mg orally every 3 days). All patients had assessable disease and endocrine-sensitive tumors, as defined by a previous positive response to endocrine therapy. There were no objective responses. Six patients had disease stabilization and nine had progressive disease on treatment. Seven patients were given endocrine therapy after gestrinone and three have responded. Gestrinone has no significant antitumor activity in hormone-sensitive breast cancer. This, however, does not preclude its use in benign breast disease, particularly since other agents used for benign breast disease can mask occult primary carcinoma.