Investigators at the Massachusetts Institute of Technology (MIT) have found that women who begin getting annual mammograms at age 40 years are healthier than the population of 40-year-old women as a whole, with a lower incidence of breast cancer than those who do not begin screenings until later.

The value of mammograms at age 40 has been debated, with just about 35% of women beginning at that age. According to MIT, mammograms for women in their 40s catch relatively few cases of breast cancer, often generate positive results, and produce some cases of unnecessary treatment. Because of these concerns, the US Preventive Services Task Force recommended in 2009 that women start regular mammogram screening at age 50 years, not 40.

The study authors noted, however, that simply changing age recommendations is not an optimal way to make breast cancer screening policies without other interventions. Given that women who opt in to testing in their 40s are relatively healthier, changing the age guidelines has a relatively limited impact. On the other hand, if mammogram screenings reached more women from ages 40 to 49, the authors said those tests would likely detect more cases per screening than they currently do.

“Debates over when to recommend screening are missing a key point,” said economist and co-author Amy Finkelstein, PhD, in a prepared statement. “There are arguments about what the costs and benefits are of screening women at a certain age, but these tend to overlook the fact that those who follow the recommendations differ from the rest of the population. This makes the problem more complicated. You can’t just forget human behavior and human selection when designing recommended health care policies.”

The authors said targeting screening to high-risk groups who are less compliant with recommendations could be more effective than general age-based recommendations. Health insurance data show than about 90% of mammograms for middle-aged women are negative, 9.7% are false positives, and just 0.7% are authentically positive, and previous studies have found limited benefits for women ages 40 to 49.

To further investigate the problem, the investigators used a clinical model of breast cancer disease progression in the absence of treatment, which had been developed by medical researchers. They used multiple sources of data to approximate the overall incidence of breast cancer in the entire population, including individuals who are not screened.

In total, they found that 10% of women who start having mammograms before age 40 have a relatively high positive test rate of 0.84%, potentially because they experience symptoms leading to the mammogram. In contrast, just 0.56% of the women who started getting mammograms at age 40 test positive, and the number of late-stage cases among them decreases by 6 percentage points compared to people who get screened before age 40.

The team also considered women who do not get mammograms even when they are recommended above age 40. Compared to this group, compliers are also more likely to get other forms of preventive care, including flu shots and cervical cancer screenings, and have fewer emergency room visits for any reason. Although they said it is more difficult to assess the incidence of breast cancer among noncompliers, the clinicians’ model suggests that the risk among these unscreened women is likely higher than it is among compliers.

Based on these findings, the study authors said screenings should be targeted to higher-risk groups, potentially based on factors such as the age of mothers at first birth or genetic markers. However, they still noted that age-based guidance can hold value, and other methods require further research.

“When you make age-based recommendations, it looks like the people who are most likely to follow them are the ones for whom it’s least beneficial—which doesn’t mean it’s not beneficial, but those are not the people you most want to target,” Finkelstein concluded.

Can mammogram screening be more effective? [news release]. MIT; December 17, 2020. Accessed December 18, 2020.