Breast cancer occurs when cells in the breast begin to grow abnormally. They do not respond to regular cell growth, division, and death signals like they are supposed to. They also don’t organize normally. Instead they grow into a tumor, which may invade surrounding layers of breast tissue and possibly spread to other organs.
Although breast cancer primarily affects women, it can also occur in children and men. For the most part, the content in this section is directed at females, who make up 99 percent of all breast cancer patients. But most of the information applies to males as well.
According to the American Cancer Society (ACS), in the United States breast cancer is the second most common cancer in women (after skin cancer) and the second leading cause of cancer death in women (after lung cancer). ACS estimated that 290,170 new cases of breast cancer (in situ and invasive cancers) were diagnosed among women in this country in 2012.
Over a woman’s lifetime, there’s a one in eight chance she will get breast cancer. For men, the lifetime risk is much lower—about one in 1,000. Breast cancer can be a highly curable disease if detected and treated early.