Oral High-Dose Progestins as Treatment for Advanced Breast Cancer

Fifty-two postmenopausal, previously treated advanced breast cancer patients who received oral high-dose progestins (medroxyprogesterone acetate [MPA] and/or megestrol acetate [MA]) were retrospectively reviewed. MPA was given to 45 patients and MA to 17 (10 earlier treated with MPA); 48 were evaluable for clinical response to progestin treatment, 43 for MPA and 5 for MA. Two complete responses and 10 partial responses (25%) with median duration of 9.5 months were seen. Forty percent of the patients obtained stable disease ≥6 months with a median duration of 8.0 months. in patients with estradiol receptor positive (n=31) and estradiol and progesterone receptor positive (n=19) tumors the response rates were 35% and 37% respectively. No differences in serum levels of MPA or MA were observed in the different responding groups. the serum levels of MA were twice as high as MPA in spite of a dose of 160 mg/day of MA compared to 1000 mg/day of MPA. A long disease-free interval, and positive receptor status of primary or metastatic lesions seemed to predict response to endocrine therapy even late in a therapeutic sequence. Side effects occurred in 11/45 (24%) of MPA treated patients and in 1/15 (7%) of MA treated patients. No difference in serum levels of MPA was found between patients with side effects and patients without side effects.