April 3, 2000 (Chantilly, Va.) -- Medical experts say there are several reasons why a mammogram may fail to detect a cancerous tumor:
The technology. Mammograms involve squeezing a woman's breast between two plates of glass -- a technique that is awkward at best. Old or badly maintained equipment and poorly trained technicians can increase the odds of an inaccurate film.
The quality of a woman's breast. Mammograms aren't good at detecting cancers in breast tissue that is dense or fibrous, as is common among female athletes and premenopausal women.
The pace of medicine. With radiologists under pressure to read more films more quickly, the risk of making mistakes has grown.
Studies on mammogram accuracy show that screenings miss anywhere from 5% to 17% of abnormalities. Yet many patients continue to believe that a "clear" mammogram is the same as a clean bill of health.
"Even though there is no perfect test, and no perfect doctor, and no perfect reading, patients expect perfect results,'' says Phan Huynh, M.D., a breast imaging specialist at the University of Texas Health Science Center in Houston.
Michael D. Towle writes regularly for WebMD on health and legal issues.