Overdiagnosis is a problem in breast cancer screening via mammograms, but experts can’t agree on how often it occurs. One of the most cited estimates comes from a 2012 New England Journal of Medicine article analyzing US data from 1976 through 2008, which concluded that breast cancer is overdiagnosed in about 31 percent of breast cancer cases. However, a new study published March 1 in Annals of Internal Medicine suggests that overdiagnosis may not be as big of a problem as the NEJM paper suggests.
Lead author Marc D. Ryser, PhD, of Duke University and his colleagues analyzed data from 82,677 mammograms and 718 breast cancer diagnoses collected from 35,986 US women aged 50 to 74 years at their first mammogram screening between 2000 and 2018. The authors found that:
- Among all preclinical cancer cases, 4.5 percent were estimated to be nonprogressive.
- In total, 15.4 percent of screen-detected cancer cases were estimated to be overdiagnosed, with 6.1 percent due to finding indolent or slow-growing preclinical cancer and 9.3 percent due to finding progressive preclinical cancer in women who would have died of unrelated causes before their diagnosis.
Based on these results, the analysis projected that one in seven cases of screen-detected breast cancer in women aged 50 to 74 years who undergo biennial screening is overdiagnosed.
A key limitation to the study, the authors note, is that it excluded women who received their first mammogram outside of a Breast Cancer Surveillance Consortium facility.
However, though it may not occur as frequently as earlier research shows, breast cancer overdiagnosis is still an issue. According to information from Breastcancer.org, around 13 percent of US women will develop breast cancer during their lifetimes and 287,850 new cases of invasive and 51,400 new cases of noninvasive breast cancer are expected to be diagnosed this year. If even a small percentage of those cases is overdiagnosed, that means that potentially tens of thousands of women will undergo unnecessary treatment.
Screening is important to prevent breast cancer deaths. Breastcancer.org predicts 43,250 American women will die from the disease in 2022. While that number is high, the death rate from breast cancer has been dropping by about 1 percent per year from 2013 to 2018, believed to be due to screening efforts to detect the disease earlier, as well as new treatments.
The results of the Annals of Internal Medicine study should, however, help people make more informed decisions regarding breast cancer screening, as noted by the authors.
To learn more, see the full article in Diagnostic Testing & Emerging Technologies, a publication from CLM’s sister brand, G2 Intelligence.