Mastectomy is the medical term used for the surgical removal of one or both breasts, either partially or completely. Mastectomy is usually performed to treat breast cancer, however in some cases, individuals believed to be at high risk of developing breast cancer can choose to have the procedure as a preventative measure. Both mastectomy and lumpectomy are referred to as localised therapies (treating the localised cancer) for breast cancer, as opposed to systemic (affecting the whole body) therapies, such as chemotherapy.

Historically, the whole breast was removed in a mastectomy, however with current practices, doctors now take into account various factors including breast size, number of lesions, position of the lesions, aggressiveness of the cancer and the emotional and cosmetic wellbeing of the patient, before deciding how much of the breast to remove. In current practice a mastectomy may or may not involve the removal of the nipple and areola. This practice of not removing the nipple and areola is dependant of several factors, both medical and aesthetic, and is known as a nipple-sparring mastectomy.