The Risk of Breast Cancer Over-Diagnosis With Mammography
Screening for cancer uses available tools to identify cancer before any detectable symptoms are present.
Screening, however, is far from perfect—an existing cancer may not be detected or the test may indicate a cancer when one does not exist. Another possible problem is over-diagnosis. This occurs when a correctly detected cancer will never become symptomatic in a person’s lifetime, leading to anguish and unnecessary treatment. Studies have found that the rate of over-diagnosis with mammography is anywhere from 5% to 50%. A study published online in the March 2006 issue of the British Medical Journal evaluated the rate of over-diagnosis with mammography.
About the Study
The study used data from a large breast cancer screening trial conducted in Sweden, which included more than 40,000 women aged 45-69 and lasted 10 years. The women, grouped as aged 45-54 and 55-69, were randomized to receive screening with mammography or not.
Researchers followed participants for 15 years after the initial trial ended and used national registries to track breast cancer detection and survival. The research team found that the rate of over-diagnosis of breast cancer was 10% in women who were screened at age 55-69 years, compared with an unscreened control group. This means that 1 in 10 women in the study would never have been harmed by her breast cancer had it not been detected by screening.
How Does This Affect You?
The American Cancer Society recommends that women get a mammogram every year, starting at age 40. Do these study results suggest that you should forgo your annual mammogram? No. Screening is an important way to detect breast cancer before it can be felt, when it is more likely to be small and still confined to the breast. Mammography may not be perfect, but at the moment, it’s the best we’ve got. However, before undergoing a mammogram, or any screening test, you should know that it is not unusual for a result to be wrong or irrelevant to your health.
Another important message from this study is that a sizable fraction of women with breast cancer live many years with no ill effects, even without treatment. While breast cancer is a scary disease that all women and their families would rightly wish to avoid, it may be comforting to know that some breast cancers cause little harm. The difficulty arises in distinguishing which cancers are harmless and which are not.
American Cancer Society
National Cancer Institute
Y-Me National Breast Cancer Organization
Dixon JM. Screening for Breast Cancer. British Medical Journal . 2006;332:449-500.
Møller H, Davies E. Commentary: Over-diagnosis in breast cancer screening. British Medical Journal . 2006;332.
What are the key statistics for breast cancer? American Cancer Society Web site. Available at: http://www.cancer.org/docroot/cri/content/cri_2_4_1x_what_are_the_key_statistics_for_breast_cancer_5.asp?sitearea=cri . Accessed March 7, 2006.
Updated breast cancer screening guidelines released. American Cancer Society Web site. Available at:
NWS_1_1x_Updated_Breast_Cancer_Screening_Guidelines_Released.asp. Accessed March 8, 2006.
Zackrisson S, Andersson I, Janzon L, Manjer J, Garne JP. British Medical Journal . 2006;332.
Last reviewed Mar 9, 2006 by
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
Copyright © 2007 EBSCO Publishing All rights reserved.