Starting Mammogram at 40 May Backfire Due to False Positives

Hi, everyone. I’m Dr Kenny Lin. I am a family physician and associate director of the Lancaster General Hospital Family Medicine Residency, and I blog at Common Sense Family Doctor.
Earlier this year, I wrote a Medscape commentary to explain my disagreement with the US Preventive Services Task Force (USPSTF)’s updated recommendation that all women at average risk for breast cancer start screening mammography at age 40. The bottom line is that when the evidence doesn’t change, the guidelines shouldn’t change. Since then, other screening experts have criticized the USPSTF guideline on similar grounds, and a national survey reported that nearly 4 out of 10 women in their 40s preferred to delay breast cancer screening after viewing a decision aid and a personalized breast cancer risk estimate.
The decision analysis performed for the USPSTF guideline estimated that compared with having mammography beginning at age 50, 1000 women who begin at age 40 experience 519 more false-positive results and 62 more benign breast biopsies. Another study suggested that anxiety and other psychosocial harms resulting from a false-positive test are similar between patients who require a biopsy vs additional imaging only. Of greater concern, women who have false-positive results are less likely to return for their next scheduled screening exam.
A recent analysis of 2005-2017 data from the US Breast Cancer Surveillance Consortium found that about 1 in 10 mammograms had a false-positive result. Sixty percent of these patients underwent immediate additional imaging, 27% were recalled for diagnostic imaging within the next few days to weeks, and 13% were advised to have a biopsy. While patients who had additional imaging at the same visit were only 1.9% less likely to return for screening mammography within 30 months compared with those with normal mammograms, women who were recalled for short-interval follow-up or recommended for biopsy were 15.9% and 10% less likely to return, respectively. For unclear reasons, women who identified as Asian or Hispanic had even lower rates of return screening after false-positive results.
These differences matter because women in their 40s, with the lowest incidence of breast cancer among those undergoing screening, have a lot of false positives. A patient who follows the USPSTF recommendation and starts screening at age 40 has a 42% chance of having at least one false positive with every-other-year screening, or a 61% chance with annual screening, by the time she turns 50. If some of these patients are so turned off by false positives that they don’t return for regular mammography in their 50s and 60s, when screening is the most likely to catch clinically significant cancers at treatable stages, then moving up the starting age may backfire and cause net harm.
The recently implemented FDA rule requiring mammography reports to include breast density could compound this problem. Because younger women are more likely to have dense breasts, more of them will probably decide to have supplemental imaging for cancer. I previously pointed out that we don’t know whether supplemental imaging with breast ultrasonography or MRI reduces cancer deaths, but we do know that they increase false-positive results.
I have personally cared for several patients who abandoned screening mammography for long stretches, or permanently, after having endured one or more benign biopsies prompted by a false-positive result. I vividly recall one woman in her 60s who was very reluctant to have screening tests in general, and mammography in particular, for that reason. After she had been my patient for a few years, I finally persuaded her to resume screening. We were both surprised when her first mammogram in more than a decade revealed an early-stage breast cancer. Fortunately, the tumor was successfully treated, but for her, an earlier false-positive result nearly ended up having critical health consequences.