One in seven women who are diagnosed with breast cancer after a mammogram with no previous symptoms are overdiagnosed and likely overtreated, according to a new estimate from researchers at Duke University.
The new estimate published in the Annals of Internal Medicine on Monday provides doctors and their patients a closer estimate of how likely women will end up dying of other causes than their diagnosed breast tumors.
"The real harm comes in this: every woman with breast cancer gets a lot of pretty harmful invasive treatments, and for a woman with overdiagnosed breast cancer, it's all for naught," said Marc D. Ryser, lead author and assistant professor in the department of population health sciences at Duke University. "She does not derive any benefit, because she would never have known about it, and she would have died with it, but not from it. She was made a cancer patient for no reason."
The study has long been in the works, following research published ten years ago that found 25% of all breast cancers found through a mammogram were overdiagnosed. Other previous estimates of overdiagnosis ranged up to 54%.
The Duke study's estimated 15.4% overdiagnosis rate is the first step in providing clinicians with information that will help patients make more informed decisions about their treatment, according to Ruth B. Etzioni, a biostatistician and professor in the Public Health Sciences Division at Fred Hutchinson Cancer Research Center.
"The frontier of really dialing down treatment is where it's at right now," Etzioni said, adding that their estimate is an average, and does not take into account the overall health of a woman, the type of tumor or other factors that should influence decision making. "There is no good predictive model for that progression."
The researchers from the study are working on such a model. Other authors are also conducting a randomized trial that is monitoring the outcomes of women with early, low-risk breast cancer and their treatment decisions.
The overdiagnosis rate increased from 11.5% at the first screening at age 50, to 23.6% by the last screening at age 74. The researchers used the records of 35,986 women part of the Breast Cancer Surveillance Consortium, which collected information based on mammography facilities and other data sources between 2000 and 2018. The median age at first screening was 56, and on average women received 2.3 screenings, which totaled 82,677 mammograms. A total of 718 breast cancers were diagnosed, including 80% that were invasive, and almost 20% that were in the very earliest stages.
Under current U.S. guidelines, mammograms should be optional for women aged 40 to 44, and then done annually from ages 45 to 54. Women 55 and older are then switched to biannual, and can continue until they have a life expectency of less than a decade left. Mammograms have also increased in cost over the years as new technology is introduced.