Tamoxifen is a hormone therapy medication used in breast cancer treatment. It works by blocking the effects of estrogen in breast tissue. This medication helps prevent breast cancer cells from growing and dividing. It belongs to a class of drugs called selective estrogen receptor modulators (SERMs).

Endoxifen is an active metabolite that forms in the body after taking tamoxifen. It is considered one of the most important compounds that makes tamoxifen effective in treating breast cancer. The body creates endoxifen when it processes tamoxifen, and the levels of endoxifen in the body are important for the medication’s effectiveness.

Breast cancer – A disease that occurs when cells in the breast tissue begin to grow abnormally and divide more rapidly than healthy cells. It typically starts in the cells of the lobules (milk-producing glands) or the ducts (passages that drain milk from the lobules to the nipple). As the cancer grows, cells can invade nearby healthy breast tissue and can travel through the lymphatic system or bloodstream to other areas of the body. The disease can develop in both women and men, though it’s much more common in women. Breast cancer may present as a painless lump, changes in breast size or shape, or changes in the skin over the breast.