What is a screening mammogram? A screening mammogram is an x-ray of the breast used to detect breast changes in women who have no signs or symptoms of breast cancer. It usually involves two x-rays of each breast. With a mammogram, it is possible to detect microcalcifications (tiny deposits of calcium in the breast, which sometimes are a clue to the presence of breast cancer) or a tumor that cannot be felt. When does the National Cancer Institute (NCI) recommend that women have screening mammograms? Women in their 40s and older should have mammograms every 1 to 2 years. Women who are at higher than average risk of breast cancer should talk with their health care providers about whether to have mammograms before age 40 and how often to have them. What are the benefits of screening mammograms? Several large studies conducted around the world show that breast cancer screening with mammograms reduces the number of deaths from breast cancer for women ages 40 to 69, especially those over age 50. Studies conducted to date have not shown a benefit for regular screening mammograms, or for a baseline screening mammogram, in women under age 40. What are some of the limitations of screening mammograms? Finding cancer does not always mean saving lives—Even though mammography can detect tumors that cannot be felt, finding a small tumor does not always mean that a woman’s life will be saved. Mammography may not help a woman with a fast-growing or aggressive cancer that has already spread to other parts of her body before being detected. False Negatives—False negatives occur when mammograms appear normal even though breast cancer is present. Overall, mammograms miss up to 20 percent of the breast cancers that are present at the time of screening. False negatives occur more often in younger women than in older women because the dense breasts of younger women make breast cancers more difficult to spot in mammograms. As women age, their breasts usually become more fatty (and therefore less dense), and breast cancers become easier to detect with screening mammograms. False Positives—False positives occur when mammograms are read by a radiologist as abnormal, but no cancer is actually present. Although all abnormal mammograms should be followed up with additional testing (a diagnostic mammogram, ultrasound, and/or biopsy), most abnormalities turn out not to be cancer. False positives are more common in younger women, women who have had previous breast biopsies, women with a family history of breast cancer, and women who are taking estrogen (for example, hormone replacement therapy).