EBM Focus: When to Begin Breast Cancer Screening; The Devil is in the Details

Practice Point: Black women have significantly higher risk for breast cancer mortality and would likely benefit from mammography screening starting at age 40. For other women, the data is less clear.

EBM Pearl: When considering the “average” risk of a disease in a population, remember that the risk may vary widely in distinct subpopulations.

Breast cancer screening with mammography in women of average risk has been the subject of much controversy over the years. Mammography decreases breast cancer-specific mortality for women aged 50-79, and most guidelines recommend mammography screening for women aged 50-74 every one-two years. That part is clear. But for women aged 40-49, there is uncertainty about the benefits and harms of screening. Robust data is lacking and as a result, screening recommendations differ significantly across guideline organizations. Some recommend starting screening as early as age 40, others at age 50, and still others are somewhere in between. All groups advise some degree of shared decision making.

In 2016, the United States Preventive Services Task Force (USPSTF) recommended against ROUTINE breast cancer screening for women aged 40-49 but advised screening every two years if requested by an informed patient. However, this group released a proposed update to this recommendation in May 2023  (a Draft Recommendation Statement) recommending that ALL women of average risk begin screening at age 40. Why the drastic change?

Recent data suggests that the risk of breast cancer is not the same across racial and ethnic groups. An article on race and ethnicity-adjusted age recommendations in JAMA Network Open examined breast cancer rates among five groups of women: White, Black, American Indian/Alaskan Native, Hispanic, and Asian/Pacific Islander. While breast cancer mortality is decreasing in general, it varies by group. For those aged 40-49 years the annual mortality rate was 27 per 100,000 Black women, 15 per 100,000 White women, and around 11 per 100,000 women in the remaining groups.

This means that a 42-year-old Black woman has the same chance of dying from breast cancer over the next 10 years as a 51-year-old White woman, a 57-year-old American Indian/Alaska Native or Hispanic woman, or a 61-year-old Asian or Pacific Islander woman. Waiting to begin screening until age 50 may be part of the reason Black women have higher breast cancer mortality. This indicates that Black women may benefit from initiating screening sooner, at age 40.

Soon after the JAMA article was published, the USPSTF released its draft update to their breast cancer screening guidelines (though their proposal was not likely informed by the JAMA article). If the draft does not undergo significant changes, USPSTF will be issuing a Grade B Recommendation for biennial screening of all women ages 40-74 years. The Grade B Recommendation indicates either a high certainty of moderate net benefit or a moderate certainty of moderate-to-substantial net benefit.

In debates over cancer screening, the harms associated with screening are often ignored. False positive test results and overdiagnosis are two obvious downsides to increased screening.

• Overdiagnosis refers to cancers which are diagnosed but would not have become clinically evident in the absence of screening.
• Some estimates for the rate of overdiagnosis from mammographic screening are as high as 15 percent.

Clearly, when to initiate breast cancer screening is an area for ongoing shared decision making. While it may make sense to start screening at age 40 for women at increased risk, and it appears that Black women should be considered at increased risk, whether this applies to all women remains to be seen.

For more information, see the topic Risk Factors for Breast Cancer in DynaMed.

Reference: JAMA Netw Open. 2023 Apr 3;6(4):e238893