Mammography: Risks of False Positive Results and Overdiagnosis

Dr. Lydia  Pace, MD, MPH Division of Women’s Health, Brigham and Women’s Hospital Boston, Interview with:
Dr. Lydia  Pace, MD, MPH

Division of Women’s Health, Brigham and Women’s Hospital
Boston, Massachusetts What are the main findings of the study?

Dr. Pace: We reviewed the existing literature about the benefits and harms of mammography, focusing on the reduction of breast cancer deaths associated with mammography, as well as the two most often-discussed harms: false positive results and overdiagnosis. We also reviewed the literature about interventions to help patients make informed decisions. We found that the literature suggests that routine screening mammography does reduce mortality associated with breast cancer, across all age groups. However, it is also associated with high rates of false positive results, and considerable rates of overdiagnosis. Overdiagnosis is the most concerning potential risk of mammography screening. Overdiagnosis is the detection of a tumor through screening that would never have caused problems for a patient. It occurs either because of a very slow-growing tumor, or because a woman has medical problems (or is old enough) such that she will likely die of another cause before the cancer became apparent. Overdiagnosis is concerning because we cannot know when a cancer is overdiagnosed, and thus a patient who is overdiagnosed will receive unnecessary treatment for cancer. The scientific literature on mammography is complex, and there are important limitations to the studies both of mammography’s benefits and harms. However, we feel that the best available data suggest that among 10,000 50 year old women undergoing annual mammography for 10 years, 5 deaths will be averted through screening mammography, while about 6130 women will experience at least one positive result. Furthermore, there is about a 19% chance that, if that woman is diagnosed with cancer detected by a mammogram, that cancer is one that would never have caused her problems. Lastly, our review showed that we need more studies to guide us in how an individual woman’s risk should dictate her mammography decisions, and how to support women in making those decisions. However, we know that most women with higher risk for breast cancer will experience higher benefit from mammography screening. any of the findings unexpected?

Dr. Pace: When we pulled together the data, the results appeared particularly disappointing in terms of what they tell us about mammography’s benefits, since the number of deaths averted through screening is so much lower than the number with false positives or the number overdiagnosed. However, it is clear that the meaning and importance of those harms could vary dramatically from woman to woman depending on her own values and preferences. What should clinicians and patients take away from your report?

Dr. Pace: When discussing mammography screening, clinicians should assess patients’ individual risks for breast cancer, for example using the National Cancer Institute’s Breast Cancer Risk Assessment tool ( as a starting point. They should be familiar with the risks and benefits of mammography screening, and should inform their patients about these, and support a patient in integrating this information into their own values.

I would advise any woman considering mammography screening, especially a woman under 50, to first discuss her own breast cancer risk with her doctor. Her doctor should discuss both the benefits and possible harms of mammography screening, and how her own risk factors might affect those benefits and harms. And she should think about what those possible harms would mean to her. She should also consider how she might feel if she decided not to be screened, and then were diagnosed with cancer, even though unfortunately the likelihood that the mammogram would have made a difference is fairly small. What recommendations do you have for future research as a result of this study?

Dr. Pace: We need more data to help us understand the magnitude of overdiagnosis from mammography screening. We also need more research to guide development of decision support tools, which can help both physicians and patients in making mammography decisions. Lastly, we need research to help us develop better breast cancer screening tests.


Pace LE, Keating NL. A Systematic Assessment of Benefits and Risks to Guide Breast Cancer Screening Decisions. JAMA. 2014;311(13):1327-1335. doi:10.1001/jama.2014.1398.