Cancer is a disease in which cells in the body grow out of control. When cancer starts in the breast, it is called breast cancer. Except for skin cancer, breast cancer is the most common cancer in American women.

Cancer support groups can provide valuable benefits for people with cancer and those touched by the disease. 

An overview from the National Cancer institute with explanations about what cancer is, how cancer cells differ from normal cells, and genetic changes that cause cancer to grow and spread.