The Breast Of Intentions: Analyzing The USPSTF’s Mammography Shift
The US Preventative Services Task Force Recently Changed Its Mammography Recommendations, Are They Correct? (From the NEJM, 2023)
The US Preventative Services Task Force (USPSTF) recently changed its recommendation for the starting age for mammography screening from 50 to 40 years. Previously, the task force recommended screening in 40- to 50-year-old women as a personal choice. This recommendation could easily become a healthcare performance measure with an imperative that primary care physicians comply.
Is there no evidence that prompted this change? Has the mortality from breast cancer increased? In our last blog post, we showed to the contrary, that there has been a steady decrease in breast cancer mortality in the United States! Moreover, the reduction in death rate has been most pronounced among women under the age of 50. This same pattern has been seen in other high-income countries including those where screening of women for breast cancer in their 40s is rare (Denmark and the United Kingdom) as well as in countries where screening is rare in all age groups (Switzerland). This might suggest that the decline in the death rate has resulted largely from improvement in treatment as opposed to an increase in screening.
Secondly, is there evidence now that did not exist before that the benefit of mammography is increasing? Since the prior USPSTF recommendations, there have been no new randomized trials of screening mammography for women in their 40s. Eight randomized trials for women in this age group, including the most recent UK Age trial, revealed no significant effect. This might suggest that screening reduces mortality less than was hoped, possibly because more aggressive disease occurs in this age group. Faster-growing cancers are more likely to be missed by screening, often appearing in the interval between exams.
Without new trial data, the USPSTF relies on statistical models that estimate what might happen if the starting age were lowered. Woloshin et al. (NEJM, Sept 2023) suggests that the models assume that screening mammography reduces breast cancer mortality by about 25% and conclude that screening 1000 women from 40 to 74 years of age, instead of 50 to 74, would result in 1 to 2 fewer breast cancer deaths over a lifetime. These same researchers suggest that complex statistical modeling can be problematic. Estimated effects can be extremely sensitive to modeling assumptions, which often reflect the conventional wisdom at the time. Models have a great deal of appeal however they are only as reliable as their input data and assumptions. For instance, a 25% relative risk reduction can be problematic and misleading since they contain no information about the absolute risk reduction which is already low and steadily decreasing for this age group. The table above shows that for US women in their 40s, the risk of death from any cause in the next 10 years is about 3% regardless of screening. The authors also point out that in the United States with screening, the likelihood of not dying from breast cancer in the next 10 years would increase from 99.7% to 99.8%. The most common outcome of mammography in this age group is false alarms. The USPSTF model estimates that 36% of women 40 to 49 years of age will have at least one false alarm in a 10-year course of biannual screening. Most will require additional testing to prove that they don’t have cancer, some of which will undergo biopsy. These adverse effects do not include those women who will be over diagnosed and treated for cancer not destined to cause harm.
The Task Force makes the point that these new recommendations are a first step in the reduction of the disparity between black and white women in mortality from breast cancer. Yet, mortality in both groups has fallen by approximately half since 1990. Yet black women remain considerably more likely to die from breast cancer than white women. The screening rate for both black and white women in this age group is approximately 60% according to the National Center for Health Statistics. It is difficult to see how applying an increased rate of screening will impact mortality or diagnosis in these two groups. And certainly, more screening cannot address the underlying differences in breast cancer biology which is accepted as the most significant cause of increased mortality in the black population. The authors suggest that a change in mammography recommendations would be supported if there were evidence that breast cancer outcomes were worsening or if there were new evidence that screening younger women had clear benefits in fact, the authors suggest that neither condition applies.
Dr. Alan Stolier, MD, FACS, clinical breast oncologist, shares his expert medical perspective with a series of educational and scientific articles.