medwireNews: A modeling study based on data from the US Breast Cancer Surveillance Consortium (BCSC) has found an overdiagnosis rate of 15.4% among women aged 50–74 years undergoing biennial mammographic screening.
One-third of the overdiagnosed cases were “due to the detection of nonprogressive cancer and two thirds were due to the detection of progressive cancer that would not have progressed to clinical disease before the woman died of other causes,” say Marc Ryser, from Duke University in Durham, North Carolina, USA, and co-investigators.
They continue: “This information clarifies the risk for breast cancer overdiagnosis in contemporary screening practice and should facilitate shared and informed decision making about mammography screening.”
The researchers identified 35,986 women aged between 50 and 74 years who had their first mammography screen at a BCSC facility during 2000–2018. A total of 82,677 screening tests during this period detected 718 cases of breast cancer, the majority (74.0%) of which were invasive, while 20.0% were in situ and 6.5% were unknown.
They used a Bayesian modeling approach to estimate an overall overdiagnosis rate of 15.4% in the cohort, with 6.1% of cases attributable to nonprogressive cancers and 9.3% to progressive disease in women who would have died of a cause unrelated to breast cancer.
The overall rate of overdiagnosis rose from 11.5% at the first screen at 50 years to 23.6% at the last screen at 74 years, report Ryser and colleagues in the Annals of Internal Medicine.
Moreover, “[t]he relative contributions to overdiagnosis from the detection of nonprogressive and progressive types of preclinical cancer [also] differed by screening round,” they add.
Specifically, the rate of overdiagnosis attributable to nonprogressive cancer was 8.4% at the first screen and 5.4–5.5% at later screens. But the rate ascribed to progressive cancer was 3.1% at the first screen, rising subsequently to 6.2%, 11.3%, and 18.1% at the fifth, ninth, and final screen, respectively.
Ryser and team additionally estimated the overdiagnosis rate for an annual screening frequency, finding a similar overall rate of 14.6%, “with patterns similar to those under biennial screening.”
They also conducted “a range of sensitivity analyses that confirmed the overdiagnosis predictions were largely insensitive to variations in both model structure and prior distributions.”
The authors of a linked editorial say that “the issue of overdiagnosis from breast cancer screening remains controversial,” with the controversy “driven both by disciplinary differences in the definition of overdiagnosis and uncertainty about the probability of overdiagnosis.”
Although they believe the current study “offers an important step forward in addressing the latter concern,” the editorialists say that eliminating overdiagnosis requires “substantial advances.”
Felippe Marcondes and Katrina Armstrong, both from Massachusetts General Hospital in Boston, USA, highlight the need for “better information about which tumors will progress” and improvements in screening technologies to “both reduce the risk for overdiagnosis and improve the ability to detect breast cancer that is currently missed by mammography.”
They conclude that the key to navigating the tradeoffs between the pros and cons of screening “remains open and effective physician–patient communication, rigorous evaluation of all proposed screening strategies, and continued investment in early detection research.”
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