In comparison, regular screening of 10,000 women age 50 would save about 37 lives. In some cases, finding a breast tumor early may mean that a woman can choose surgery that saves her breast. Also, a woman whose breast tumor is detected in its early stages may not have to undergo chemotherapy. 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. False positives are more common in younger women than older women. About 97 percent of women ages 40 to 49 who have abnormal mammograms turn out not to have cancer, as compared with about 86 percent for women age 50 and older.