Breast cancer overdiagnosis rate ‘not as alarmingly high’ as reported among certain women
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An estimated 1 in 7 screen-detected breast cancers in biennially screened women aged 50 to 74 years will be overdiagnosed, according to an analysis of an authoritative U.S. population data set published in Annals of Internal Medicine.
The risks for breast cancer overdiagnosis in contemporary screening practices should facilitate shared and informed decision-making on mammography screening, researchers wrote.
“Breast cancer is a very heterogeneous disease and ranges from slow-growing indolent tumors to very aggressive lethal cancers. Because the risk [for] overdiagnosis is highest for screen-detected tumors on the more indolent end of the spectrum, it is important to explicitly account for nonprogressive tumors when estimating the rate of overdiagnosis,” Marc D. Ryser, PhD, assistant professor in population health sciences and member of Duke Cancer Institute at Duke University, told Healio.
Methodology
The analysis included 35,986 women aged 50 to 74 years (median age, 56 years; 55.6% white) who received at least one screening mammogram at a Breast Cancer Surveillance Consortium facility between 2000 and 2018.
Ryser and colleagues estimated overdiagnosis indirectly through Bayesian inferences. They used data on screen and interval cancer incidence to estimate underlying latency and fraction of indolent cancer. Based on those estimates, along with life tables on the risk for death of causes other than breast cancer, they predicted the extent of overdiagnosis among a cohort of women undergoing regular mammography screening.
Estimating the rate of overdiagnosis in this setting, accounting for the detection of nonprogressive cancer, served as the primary objective.
Key findings
The results included data from 82,677 mammograms and 718 breast cancer diagnoses.
The analyses showed 4.5% (95% uncertainty interval [UI], 0.1-14.8) of all preclinical cancer cases estimated as nonprogressive cancer. Additionally, in a program of biennial screening from ages 50 to 74 years, researchers calculated a predicted overdiagnosis rate of 15.4% (UI, 9.4-26.5) among screen-detected cancer cases, including 6.1% (UI, 0.2-20.1) due to detecting indolent preclinical cancer and 9.3% (UI, 5.5-13.5) due to detecting progressive preclinical cancer in women who would have died of an unrelated cause before clinical diagnosis.
Ryser told Healio that results indicate breast cancer overdiagnosis is “not as alarmingly high” as previously reported.
“We have long known that the most prominent estimates of breast cancer overdiagnosis in the U.S. were inflated. For example, a widely cited figure is that 30% of all breast cancers are overdiagnosed, which translates into an even higher percentage among cancers detected by screening,” Ryser said. “So, we were not surprised that our number was lower.”
Implications
Ryser noted that the current calculations apply to women of average health, which could open the door to further research.
“In practice, people who are routinely screened for cancer tend to be of better health than average, and their risk for overdiagnosis will likely be lower than 1 in 7 screen-detected cases,” Ryser told Healio. “To obtain more personalized estimates of overdiagnosis, a person’s health status, as well as other features such as breast density and race, will need to be accounted for.”
The current research offers “an important step forward” in addressing the probability of overdiagnosis, Felippe O. Marcondes, MD, research fellow in medicine at Massachusetts General Hospital, and Katrina Armstrong, MD, formerly of Harvard Medical School and currently CEO of Columbia University Irving Medical Center, executive vice president for health and biomedical sciences, and dean of the faculties of health sciences and medicine, wrote in an accompanying editorial.
Although screening can be beneficial in detecting disease when it’s easier to treat, “the risk of labeling millions of persons as having a disease without improving their outcomes is very real,” they wrote.
“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. We look forward to the day when making an early diagnosis always helps our patients achieve better outcomes,” Marcondes and Armstrong wrote.
References:
Marcondes FO, et al. Ann Intern Med. 2022;doi:10.7326/M22-0483.
Ryser MD, et al. Ann Intern Med. 2022;doi:10.7326/M21-3577.
For more information:
Marc D. Ryser, PhD, can be reached at Duke University, 215 Morris St., Durham, NC 27701; email: marc.ryser@duke.edu.
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