What is breast cancer? Breast cancer is a type of cancer that occurs when there is an uncontrolled growth of abnormal cells in the breast. Breast cancer can spread, or metastasize to other parts of the body. Breast cancer is the most common cancer in women after skin cancer, according to the Centers for Disease Control and Prevention (Source: CDC). Less frequently, breast cancer can occur in men. When doctors diagnose breast cancer in an early stage of growth, treatment is often successful and breast cancer survival rate is high. The prognosis for later stages of breast cancer is improving with ever more advanced and targeted treatments, but breast cancer screening with mammograms at age 40 and older is key to an early diagnosis and cure. Prognosis of breast cancer depends on the type of breast cancer and the stage of advancement; your age, medical history, and coexisting conditions or diseases; and available treatments.