Progesterone receptor modulators in breast cancer

Breast cancer has been treated successfully with selective estrogen receptor antagonists (SERMs) such as tamoxifen, receptordepleting agents such as fulvestrant, and aromatase inhibitors such as anastrozole. Selective progesterone receptor modulators (SPRMs or PRMs) have not been studied as much and are currently under investigation for inhibition of mammary carcinogenesis in animal models and breast cancer prevention trials in women. They might follow tamoxifen and aromatase inhibitors in the adjuvant treatment of breast cancers with acquired resistance. These uses have not provoked ground-breaking progress or studies and PRMs do not have a high profile. Most in vitro and in vivo studies indicate that PRMs preferentially suppress cell proliferation and also induce apoptosis. In this review we summarized the data on the effects of PRMs and particularly of the antiprogestins RU-486 (mifepristone) and CDB-4124 (Progenta, Proellex or telapristone acetate) on breast cancer models. Both agents have been employed in preclinical and clinical studies for prevention and treatment of breast cancer. This author believes that PRMs should be investigated more intensely.