How Common Is Breast Cancer Overdiagnosis with Screening Mammography in Older Women?

Cancer overdiagnosis refers to cancers detected by screening that never would have caused clinically apparent disease had the screening not occurred. For women older than 70 — who might be weighing the benefits and risks of continuing breast cancer screening — there are limited data on risk of overdiagnosis with mammography.

In this U.S. study, researchers identified 54,000 women (age, ≥70) who had negative screening mammograms in 2002. The cumulative incidence of breast cancer through 2017 was compared in those who had another screening mammogram during the subsequent 3 years and those who did not.

Potential cancer overdiagnosis (the difference in cumulative breast cancer incidence between the screened and unscreened cohorts) was common in all age groups:

• Ages 70–74: 1.9 cases per 100 patients (6.1 vs. 4.2)
• Ages 75–84: 2.3 cases per 100 patients (4.9 vs. 2.6)
• Age ≥85: 1.5 cases per 100 patients (2.8 vs. 1.3)

Potentially overdiagnosed cancers accounted for 31%, 47%, and 54% of cancers in those three age groups, respectively. Importantly, screening was not associated with statistically significantly lower breast cancer mortality or incidence of regional or distant breast cancers.