Breast cancer is the leading killer of women worldwide. The majority of cases occur in postmenopausal women, but a significant number occur in younger women. One of the most important factors in successful treatment of breast cancer is early detection of suspicious lumps. Monthly self-examination of the breasts and mammography, which can identify very early, readily treatable neoplastic and preneoplastic lesions, are successful at detecting tumors at early stages. When breast cancer is diagnosed, treatment begins with surgical removal of the cancer, through either radical mastectomy (removal of the breast, associated lymph nodes, and parts of the arm and chest muscles), removal of the breast, or lumpectomy (removal of the lump and some surrounding tissue). Most patients are then given radiation therapy and/or chemotherapy treatments to make sure that all the cancer is destroyed. Chemotherapy may include the use of antiestrogens such as tamoxifen, which inhibits the growth of breast cancer cells with little or no toxicity to the patient and the remaining normal cells; it is also being used as a preventive drug.
No one cause for breast cancer has been identified, but diet is believed to play a role. Additional risk factors which increase the chance of developing breast cancer are early menarche, late menopause, and late first childbirth; these are all related to the endocrine status of the woman. A gene called BRCA1 has also been found to be associated with a significant number of cases, especially in younger women with family histories of breast cancer.