One in 7 breast cancers detected during screening are overdiagnosed

A new model, based on data from the Breast Cancer Surveillance Consortium (BCSC), suggests that overdiagnosis of screen-detected breast cancer is less frequent than estimated from excess-incidence studies. However, the model also takes indolent tumours into account and produced a higher estimate than previous models that didn’t consider this factor.

Breast cancer screening is subject to overdiagnosis, which is the mammographic detection of cancers that would not become symptomatic or otherwise cause harm in the absence of screening. Estimates of overdiagnosis based on excess incidence are prone to bias, and estimates based on models have been criticised for not explicitly accommodating indolent tumours. Dr Marc Ryers (Duke University Medical Center, NC, USA) and colleagues developed a model that accounts for the transition from healthy to preclinical and clinical disease, while allowing for a fraction of indolent preclinical tumours [1]. Based on data of 35,986 women, 82,677 screens, and 718 breast cancer diagnoses, the predicted overdiagnosis rate among screen-detected cases was 15.3% (95% Prediction Interval [PI] 9.7–25.2), where 6.0% (95% PI 0.2–19.0) was due to the detection of indolent cancers and 9.3% (95% PI 5.8–13.6) was due to competing mortality [2]. For a program of annual screening from age 50–74, the overall predicted overdiagnosis rate was 14.6% (95% PI 9.4–23.9).

“Our results indicate that overdiagnosis among screen-detected cancers is less frequent than estimated by excess-incidence studies and more frequent than estimated by previous modelling studies that did not account for indolent tumours,” concluded Dr Ryser.

1. Ryser MD, et al. Am J Epidemiol. 2019;188:97–205.
2. Ryser MD, et al. Estimation of breast cancer over diagnosis in a US breast screening cohort. GS4-06, SABCS 2021 Virtual Meeting, 7–10 December.

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Posted on 31 January, 2022