Several studies have shown that regular screening mammograms can help to decrease the chance of dying from breast cancer. The benefits of regular screening are greater for women over age 50. According to the American Cancer Society, researchers report that mammograms are twice as effective as previously thought. 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 occur when mammograms appear normal even though breast cancer is actually present.
False negatives are more common in younger women than in older women.
The dense breasts of younger women contain many glands and ligaments, which make breast cancers more difficult to spot in mammograms. Screening mammograms miss up to 25 percent of breast cancers in women in their forties compared with about 10 percent of cancers for older women. Most abnormalities will turn out not to be cancer. Over a 10-year period, the chance that a woman will have a false positive mammogram is about 50 percent. False positives are more common in younger women than older women.