Breast cancer overdiagnosis may not happen as frequently as previously thought

Previous estimates of breast cancer overdiagnosis rates may have been too high, according to a modeling study.

Researchers studied data from the Breast Cancer Surveillance Consortium to estimate breast cancer overdiagnosis rates for a cohort of 35,986 women, who underwent 82,677 mammograms and had 718 breast cancer diagnoses. Women were 50 to 74 years of age and were screened between 2000 and 2018. The cohort was racially, ethnically, and geographically diverse and representative of the mammography screening population in the U.S., the study authors noted. Results were published March 1 by Annals of Internal Medicine.

With biennial screening from ages 50 to 74 years, 15.4% (95% uncertainty interval [UI], 9.4% to 26.5%) of screening-detected cancer cases were overdiagnoses—6.1% (95% UI, 0.2% to 20.1%) due to indolent preclinical cancer and 9.3% (95% UI, 5.5% to 13.5%) due to progressive preclinical cancer in women who would have died of an unrelated cause before clinical diagnosis. Among all preclinical cancer cases diagnosed, 4.5% (95% 95% UI, 0.1% to 14.8%) were estimated to be nonprogressive.

Overall, the rate of overdiagnosis among screening-detected cancer cases that was due to nonprogressive cancer decreased from 8.4% (95% prediction interval [PI], 0.3% to 26.4%) at the first screening to 5.5% (95% PI, 0.2% to 17.0%) at the last screening. Overdiagnosis from progressive disease that would not have become clinically evident before death from other causes increased from 3.1% (95% PI, 1.6% to 5.1%) at the first screening to 18.1% (95% PI, 11.9% to 24.5%) at the last screening. Increasing the screening frequency from biennial to annual yielded an overall predicted overdiagnosis rate of 14.6% (95% PI, 9.4% to 23.9%), with patterns similar to those of biennial screening.

An editorial estimated that about 7 in 1,000 women will be diagnosed with invasive or noninvasive breast cancer on the basis of a screening mammogram, and about 1 in 1,000 women who undergo mammography will be found to have a cancer that would never have caused problems. Assuming that about 60% of the 280,000 cases of breast cancer diagnosed each year are found by mammography, eliminating overdiagnosis could spare 25,000 women the cost and complications of unnecessary treatment, the editorialists said.

“Screening tests, whether for cancer or other conditions, can provide great benefit by detecting disease when it is more easily treatable,” the editorial stated. “However, the risk of labeling millions of persons as having a disease without improving their outcomes is very real. For now, the key to navigating these tradeoffs remains open and effective physician–patient communication, rigorous evaluation of all proposed screening strategies, and continued investment in early detection research.”