Mammogram

An X-ray of the breast. The breast is squeezed between two plates to compress the tissue so that X-rays will pass through it.

When You Should Have It: Medical groups recommend that women 50 and over who have no lumps or other breast abnormalities have an annual mammogram. The evidence of a benefit is not as strong for women between 40 and 50. To be safe, many doctors recommend starting mammograms at 40 and having them annually.

What It Can Tell You: Suspicious findings come in two forms, calcifications and masses. Calcifications are calcium deposits; some are normal, but certain patterns of calcification may indicate a tumor and must be biopsied. A mass may be biopsied, or it can be examined with ultrasound to find out whether it is a cyst.

Risks: False positives and false negatives. On average, a woman has a 10 to 11 percent chance with each mammogram of a finding that requires further testing but turns out to be a false positive. Among abnormal mammograms, only 3 percent turn out to have detected cancer. But there are also false negatives: Overall, mammograms fail to detect 10 to 15 percent of cancers, according to Elizabeth Morris, M.D., an associate professor of radiology at Memorial Sloan-Kettering Cancer Center, in New York City.