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Individualized risk assessment would increase mammography’s benefit
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Individualized mammography screening decisions that account for the patient’s breast cancer risk factors and personal preferences, as well as an increased understanding of the risk for overdiagnosis, would maximize the benefits derived from mammography, according to a study review.
“What I tell my patients is that the mammogram is not a perfect test,” Nancy Keating, MD, MPH, associate professor of Health Care Policy at Harvard Medical School and associate professor of medicine at Brigham and Women’s Hospital, said in a press release. “Some cancers will be missed, some people will die of breast cancer regardless of whether they have a mammogram, and a small number of people that might have died of breast cancer without screening will have their lives saved.”
Nancy Keating
To weigh the risks and harms associated with mammography for breast cancer screening, Keating and Lydia E. Pace, MD, MPH, research fellow in women’s health at Brigham and Women’s hospital, reviewed studies in the MEDLINE database from 1960 to 2014.
Overall, mammography was associated with a 19% reduction in the risk for breast cancer mortality.
The risk reduction varied among women aged 39 to 49 years (RR=0.85; 95% CI, 0.75-0.96) from those aged 60 to 69 years (RR=0.68; 95% CI, 0.54-0.87). Researchers found 1,904 women aged 39 to 49 years would need to be invited to screening to prevent one death from breast cancer, whereas only 377 women aged 60 to 69 years would need to be invited to prevent one death.
Data from the Breast Cancer Surveillance Consortium indicated the 10-year risk for false-positive results was higher among women who commenced annual screening at age 40 to 50 years compared with those aged 66 to 74 years (61.3% vs. 49.7%)
Using data from three randomized controlled trials, researchers determined 19% of cancers diagnosed among women invited to screening would be cases of overdiagnosis.
Pace and Keating wrote more accurate and personalized risk models, which include baseline cancer risk, are necessary. They suggested risk models that combine risk factors — including age at menarche, age at first birth, number of first-degree relatives with breast cancer, number of previous breast biopsies, presence of atypical hyperplasia, breast density and race/ethnicity — are more likely to accurately predict risk in population subgroups than in individual women.
A meta-analysis of four studies indicated numerical assessment of risk was not associated with the uptake of mammography among women aged at least 40 years (OR=0.84; 95% CI, 0.68-1.03). However, one randomized control trial found women aged 38 to 45 years would be less likely to initiate screening after receiving educational materials on the benefits vs. harms associated with mammography.
“While we need more research on mammography’s benefits and harms today, existing data suggest that we have been overestimating the benefits of mammography and underestimating the harms over the years,” Pace said. “It is really important to have informed discussions with our patients to help them understand the chances that a mammogram will benefit them as well as the possible downsides of getting a mammogram, so that they can incorporate their own values and preferences in making the right decision for themselves.”
Disclosure: Keating reports researching funding from the American Cancer Society, the Komen for the Cure Foundation and the NCI.
Perspective
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Tiffany P. Avery, MD
Recommendations for routine use of screening mammography among US women are an area of active controversy among the medical community and media. Mixed messages abound regarding the age to begin screening mammograms and the appropriate frequency. In the United States, screening guidelines vary by professional organization. The US Preventive Services Task Force recommends biennial screening mammograms in women aged 50 to 79 years, whereas the American Cancer Society recommends yearly mammograms starting at age 40 years.
The current study by Pace and Keating is a thorough review of prospective randomized trials investigating the value of screening mammography. This review is a useful tool for physicians who counsel women regarding the risks and benefits of using breast cancer screening. The suggestions offered for providing individual risk assessment for each patient and decision support for women who are advised to undergo screening mammograms provide a valuable outline to help patients navigate the conflicting recommendations regarding screening mammography.
The authors of the study highlight some of the shortcomings of the review. The studies regarding the impact on breast cancer-related mortality of screening were mostly conducted using data from European and Canadian populations. The generalizability of these studies to women in the United States is questionable considering the heterogeneity of the US population and differences in risk factors. For example, African-American women bear the highest breast cancer-related mortality. This is a group that would not have been represented in these studies. Moreover, difference in lifestyle among US women may also contribute to differences in incidence and outcome, suggesting complexity in evaluating population risks.
Regarding individual risks of screening, the harm of a false-positive result varies based on the individual patient and should be considered when making recommendations. Current screening methods have shown mortality benefits among all age groups, including women aged 40 to 49 years. Women aged 40 and older should be offered screening mammograms with an understanding of their individual risk and potential harms.
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