Breast cancer is the most common cancer and the second leading cause of cancer death in women in the United States, with an estimated 252,710 new cases and 40,610 deaths in 2017.1 Breast cancer mortality is prevented by the use of regular screening mammography, as demonstrated by randomized controlled trials (20% reduction), incidence-based mortality studies (38% to 40% reduction), and service screening studies (48% to 49% reduction).2
Controversy continues, however, on when to start mammography screening, when to stop screening, and the frequency with which screening should be performed for women at average risk for breast cancer. Indeed, 3 national recommendations—written by the American College of Obstetricians and Gynecologists (ACOG), the American Cancer Society (ACS), and the US Preventive Services Task Force (USPSTF)—offer different guidelines for mammography screening (TABLE 1).2–4
There are 2 principal reasons for the controversy over screening:
- mammography has both benefits and harms, and individuals place differential weight on the importance of these relative to each other
- randomized controlled trials on screening mammography did not include all of the starting age, stopping age, and screening intervals that are included in screening recommendations.
New comparison of recommendations
An ongoing project funded by the National Cancer Institute, known as the Cancer Intervention and Surveillance Modeling Network (CISNET), models different starting and stopping ages and screening intervals for mammography to assess their impact on both benefits (mortality improvement, life-years gained) and harms (callbacks, benign breast biopsies). Recently, Arleo and colleagues used CISNET model data to compare the breast cancer screening recommendations from ACOG, the ACS, and the USPSTF, focusing on the differential effect on benefits and harms.5
Benefits vs harms of screening in perspective
Without question, the principal goal of cancer screening strategies is to effectively and efficiently reduce cancer mortality. Because mammography screening has both benefits and harms, a clear understanding of the relative frequency of these events among the different screening recommendations should be an important element in patient counseling.
Based on CISNET-modeled estimates, TABLE 2, illustrates the differences in both benefits and harms of the 3 screening strategies. With all strategies, there is a clear benefit in both fewer breast cancer–related deaths and life-years gained per 1,000 women screened.
The greatest benefit is seen in the A40–84 group, that is, women who undergo the most intensive screening strategy with annual screening starting at age 40 and ending at age 84 (ACOG) compared with the USPSTF’s least intensive screening strategy, B50–74, which includes biennial screening starting at age 50 and stopping at age 74; benefits of the ACS’s H45–79 strategy (annual screening at ages 45 to 54 years then biennial screening at ages 55 to 79) were in-between. Not surprisingly, the A40–84 screening strategy was also associated with the most harms, with more recalls and benign breast biopsies; the least harms occurred with the USPSTF strategy, with the ACS strategy again in-between in terms of harms.
Breast density and optimal screening for breast cancer
To further demonstrate differences between the 3 strategies, CISNET also modeled results by looking at all women born in a single birth year cohort (1960) who were still alive at age 40 (2.468 million women). The modeling estimates the number of women who would die from breast cancer without screening mammography and compares that with the number of women who would die from breast cancer using any of the 3 screening strategies. Using this 1960 birth year cohort analysis, there would be approximately 12,000 fewer breast cancer deaths using the ACOG-recommended screening strategy compared with the USPSTF-recommended approach.4
These data show that while there are more harms associated with the most intense screening recommendation, the less frequent screening recommendations will result in higher mortality and more life-years lost. It is reasonable to assume that most patients would value mortality reduction and life-years gained over a likelihood of more benign biopsies or callbacks. As a result, each of the guidelines recommends that by age 40, women at average risk for breast cancer should be counseled and offered mammography screening based on their personal values.