Breast cancer is a condition in which cells in the breast begin growing abnormally; these cells divide rapidly and spread throughout the breast tissue, and eventually to the lymph nodes or other parts of body. Most often, breast cancer begins in the ducts that produce milk, though it may also originate in the lobules or other breast tissue.
Breast cancer is the second-leading cause of death among American women; an estimated 12 percent of American will develop the disease, and about 3.5 percent of women will die from it. It is most commonly diagnosed in women over the age of 65 (50 percent of all cases). Surprisingly, perhaps, breast cancer can also occur in men, though this is rare—less than 1 percent of breast cancer cases occur in men, usually men between the ages of 60 and 70.