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. Breast cancer screening means checking a woman’s breasts for cancer before she has any symptoms.. Mammograms are the best way to find breast cancer early, when it is easier to treat and before it is big enough to feel or cause symptoms. Most women who are 50 to 74 years old should have a screening mammogram every two years. If you are 40 to 49years old, or think you may have a higher risk of breast cancer, ask your doctor when to have a screening mammogram. Some things may increase your risk. If you have risk factors, you may be more likely to get breast cancer.