Treatment is ordinarily directed at the diseased breast and at the cancer cells that may have spread beyond the breast. Aside from skin and lung cancer, breast cancer is the most common type of cancer seen in women in the United States and in other western societies. The frequency of the disease rises with age. A woman's lifetime risk of getting breast cancer is about 1 in 250 at age 35, but rises to about 1 in 50 by age 65. Breast cancer diagnosis has increased steadily in the United States since the mid-1980s, but the death rate from breast cancer has also fallen steadily during the same period.
Breast cancer occurs in men as well as women, but is much less common.
Both the behavior of the disease and its treatment are similar to that in women. The exact way that breast cancer develops is not well understood. This is currently a major area of research. Several factors affect a woman's chance of developing breast cancer. Between 5 and10 percent of invasive breast cancer is related to the presence of a gene that confers a very high risk of developing the disease.