Why isn’t there agreement on when women need to start getting mammograms?

If, after reading the latest recommendation on breast cancer screening by the United States Preventive Services Task Force (USPSTF), you feel like your head is spinning, that’s understandable. The task force’s newest advice, which gives a “B” grade in favor of routine mammograms for women in their 40s, reverses its 2016 statement saying the test should be optional for such women. And that 2016 opinion conflicted with earlier task force recommendations.

Why has there been such zigzagging when it comes to screening younger women for signs of hidden breast cancer? It’s not that the data keep changing between task force recommendations. Instead, as with other groups using evidence-based medicine, task force reviews emerge from complicated analyses and discussions of data by experts with individual opinions about what the data do and do not show. Although this subjectivity might appear to be contradictory to evidence-based medicine, it is an inevitable part of it. And it is why the evaluation of complicated tests such as mammography remains tricky — and sometimes frustrating to the people who might need it.

One of the great ironies of the decades-old controversy over the value of mammograms for average-risk women in their 40s is the vast amount of data available to try to answer this question. (There is much broader consensus that mammograms are indicated for women between the ages of 50 and 74, for whom the task force also just gave a “B” grade, meaning it recommends that clinicians provide mammograms to eligible people based on “at least fair evidence” that mammograms in this age group improve health outcomes and the benefits outweigh harms.)

Eight randomized controlled trials of mammography, the gold standard for assessing scientific efficacy, have been conducted dating back to the early 1960s. But from the start, there were fierce debates over what the statistics showed: Was mammography in younger women an imperfect test that nevertheless saved a substantial number of lives? Or was it one that caused substantially more harms than benefits, most notably unnecessary biopsies and psychological trauma caused by false-positive results?

The USPSTF is only one of many organizations that has used evidence-based medicine to try to answer these questions about breast cancer screening. Certain groups, such as the American Cancer Society and the American College of Radiology, have historically been pro-mammography. They have placed more weight on the studies that favor the test, arguing that these data are more reliable. Other groups have been more negative, placing faith in research, such as the Canadian National Breast Screening Study, that has emphasized the harms of mammography.

USPSTF members are all generalist clinicians — not specialists, who may already have pre-existing opinions about the breast cancer screening tests being evaluated. Nevertheless, regardless of who is using the tools of evidence-based medicine, scientific data do not “reveal” answers. Rather, experts must interpret them. And there is often genuine disagreement.

A major imbroglio occurred in 1997 when the National Cancer Institute (NCI) convened a consensus conference to try to bring resolution to the debate. It did just the opposite. Its conclusion — that “the data currently available do not warrant a universal recommendation for mammography for all women in their forties” — caused an outcry. Critics termed this conclusion by a panel of qualified scientists as “fraudulent” and “tantamount to a death sentence” for women in their 40s, as I wrote in my book “The Breast Cancer Wars.” Even more remarkably, the United States Senate voted 98-0 in favor of a resolution to try to get the decision reversed, which is what the NCI’s parent agency, the National Institutes of Health, ultimately did.

Two decades later, it was the USPSTF’s turn to be blasted for its decision not to recommend routine mammograms for women between the ages of 40 and 49.

First, some background. As shown in the table below, in both 1989, five years after its founding in 1984, and in 1996, the task force had decided the data were not enough for them to weigh in on this age group. In 2002, it issued a “B” grade, saying that despite its limitations, routine mammograms were indicated for women in their 40s.

Seven years later, the task force reversed this decision, going instead with a “C” grade, meaning no recommendation for or against screening women in the 40s. Such a grade didn’t mean that mammography in younger women should not be offered to them. It just meant that, given the complicated balance between benefits and harms that existed, individuals should discuss the pros and cons with their health providers and make a personal choice.

This attempt at nuance, however, was widely misunderstood and rejected. The USPSTF had accurately stated that it recommended “against routine screening mammography in women aged 40 to 49.” But the public construed this statement as indicating that it was against the test more broadly. Critics pounced, ridiculing the “C” grade as “callous and poorly conceived” and placing “women at risk of dying unnecessarily.”

Though the USPSTF did not reverse its recommendation, as the NCI did after the consensus conference, it was contrite. After the outcry, it announced it would improve its communication efforts as well as issue drafts of its recommendations to which physicians, activists, and patients could reply. Indeed, this policy is why the task force issued a preliminary draft of its 2024 recommendation in May 2023.

What lessons can be learned from this history? Most importantly, the shifting “B” and “C” grades for breast cancer screening among younger women are, to some degree, semantics. As Russell Harris, a physician, epidemiologist, and former member of the USPSTF wrote earlier this year in the Annals of Internal Medicine, in both 2002 and 2009, the identified benefits of mammography and the identified harms of mammography had not really changed but the two different task forces interpreted them differently. In 2009, for example, great emphasis was placed on a statistic called the number needed to invite (NNI), which is basically how many women in their 40s would have to be screened in order to save one life from breast cancer. The Task Force concluded that this number — 1,904 — warranted a “C” grade given the potential harms to the other 1,903 screened women.

The current USPSTF, in deciding on a “B” grade, relied heavily on decision modeling, an increasingly common statistical tool that uses available data on factors such as breast cancer incidence, mammography performance, and treatment strategies to complement evidence from randomized clinical trials. Such data are, by definition, speculative. One finding from the modeling research — that starting screening at age 40 instead of age 50 would lead to an additional 1.3 breast cancer deaths prevented among every 1,000 women screened — nudged the task force toward its “B” grade, as did additional data suggesting that the benefit might be even greater among Black women, who have a 40% higher death rate from breast cancer than white women.

As Harris pointed out, there are no data from randomized controlled trials indicating that the effectiveness of mammography differs by race. But the current task force, understandably concerned both about increasing rates of breast cancer in younger women and high breast cancer mortality among Black women, chose to emphasize the results of the modeling studies in addition to those of the more traditional randomized trials.

Is such variability worrisome? Not necessarily. What seems clear is that for women under 50, mammography is not a great screening test. It certainly saves lives, but it isn’t as effective as screening tests such as colonoscopy and Pap testing, and leads to many false-positive results. (Indeed, the 2024 USPSTF weighed in on using breast cancer screening tests other than mammography, such as MRIs and ultrasounds, but found that there were insufficient data to assess them.)

And the reality is that, when a screening test has both substantial benefits and drawbacks, different task forces, comprised of different members, may reach different conclusions. To be sure, this phenomenon may be highly unsatisfying. Patients and their providers appreciate clarity when making clinical decisions. But with mammography for young women, there is uncertainty. The ambiguity may also have financial implications, since preventive services that get “A” and “B” grades must be covered by insurance, thanks to the Affordable Care Act. Services with “C” grades may or may not be covered.

But whether or not the USPSTF says “B” or “C,” if a woman in her 40s is having an informative and meaningful conversation with her health care provider about the pros and cons of screening mammography, that’s excellent.

Barron H. Lerner, M.D., Ph.D., is a professor of medicine and population health at New York University Grossman School of Medicine and the author of five books, including “The Breast Cancer Wars: Hope, Fear and the Pursuit of a Cure in Twentieth-Century America” (Oxford University Press, 2003). Funding for this research was provided by the Robert Wood Johnson Foundation.