Influence of tamoxifen-medroxyprogesterone sequential therapy on estrogen and progesterone receptor contents of breast cancer.

The influence of tamoxifen (TAM) and medroxyprogesterone acetate (MPA) sequential administration on the estrogen receptor (ER) and progesterone receptor (PR) contents of breast cancer was studied in 68 patients with operable breast cancer. TAM was used as a primer of PR induction in order to enhance the effects of MPA. Half of the patients (n = 34) were preoperatively treated with TAM (20 mg/day for 7 days) and sequentially with MPA (1200 mg/day for 17 (median) days). ER and PR of surgical specimens were assayed by enzyme immunoassay and the results were compared with those obtained from the other half of the patients (n = 34), who had not received any treatment before surgery. TAM-MPA treatment significantly lowered PR in the cytosol regardless of the menopausal status. On the other hand, TAM-MPA treatment significantly lowered ER in the cytosol only in the postmenopausals but not in the premenopausals. These results demonstrate that reduction of ER provoked by TAM-MPA treatment is dependent on menopausal status.