What medication is classified as a selective estrogen receptor modulator (SERM) commonly used in breast cancer treatment?

The medication classified as a selective estrogen receptor modulator (SERM) that is commonly used in breast cancer treatment is Tamoxifen. Tamoxifen works by binding to estrogen receptors on cells, particularly in breast tissue, which effectively blocks estrogen from binding to these receptors. This action is crucial because certain types of breast cancer growth are driven by estrogen, and by inhibiting estrogen's effects, Tamoxifen helps slow or stop the progression of the disease. It is primarily used in hormone receptor-positive breast cancer, making it a key option in both adjuvant therapy for early-stage disease and treatment for metastatic disease.

In contrast, the other medications mentioned are aromatase inhibitors, not SERMs. Letrozole, Anastrozole, and Exemestane all work by reducing estrogen levels in the body rather than blocking estrogen receptors directly. This distinction is important since SERMs like Tamoxifen and aromatase inhibitors have different mechanisms of action and are chosen based on the specific characteristics of the breast cancer being treated.