Breast cancer is cancer that forms in the cells of the breasts. Breast cancer can occur in both men and women, but it's far more common in women. After skin cancer, breast cancer is the most common cancer diagnosed in women in the United States. But breast cancer rates have fallen in recent years, though doctors aren't certain why. Still, for many women, breast cancer is the disease they fear most. Public support for breast cancer awareness and research funding has helped improve the diagnosis and treatment of breast cancer. Breast cancer survival rates have increased and the number of deaths has been declining, thanks to earlier detection, new treatments and a better understanding of the disease.