Breast cancer is a malignant tumor that has developed from cells at that site.
The disease occurs most frequently in women, and rarely in men. The breasts are glands protruding from the upper front chest wall. The breasts produce and release milk in women in association with pregnancy. They are composed of milk-secreting glands, ducts, and fatty, connective, and lymphatic tissue. Lobules are the glands of women's breasts that can produce milk.