Selective estrogren receptor modulators, known as SERMs, are a class of anti-cancer drugs used to block tumor growth by mimicking estrogen and thereby filling up estrogen receptors on ER+ cells. Their action is usually different in various tissues, thereby granting the possibility to selectively inhibit or stimulate estrogen-like action in various tissues.Wikipedia
The most widely used SERM is tamoxifen. Tamoxifen blocks estrogen receptors in the breast, but mimics estrogen in the uterus, which may increase the risk for uterine cancer. There is also a potential risk of stroke and pulmonary embolism (lung blood clots) for women with certain types of cancer, and for women using Tamoxifen for prevention of breast cancer. Other SERMs that are available include raloxifene (Evista) and toremifene citrate (Fareston). Toremifene has an indication for the treatment of breast cancer that is estrogen receptor positive or of unknown status. Raloxifene is currently indicated for the prevention of osteoporosis, but there are studies currently in progress to assess the usefulness of raloxifene in the treatment of breast cancer and to compare it against tamoxifen (e.g. STAR Trial). The NAFTA Trial is another trial in progress that assesses the usefulness of toremifene versus tamoxifen. None of the SERMs treat menopausal symptoms, and may in fact increase them. Additionally, all are associated with some increased risk of blood clot formation.
The SNPedia tamoxifen page contains a detailed discussion of SNPs that may influence the efficacy of tamoxifen.
Alternatives drug classes to SERMs in the treatment of breast cancer include aromatase inhibitors and progestins.