Screening Mammography Has Led to Overdiagnosis of Breast Cancer

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(ChemotherapyAdvisor)–Screening mammography “is having, at best, only a small effect on the rate of death from breast cancer.”

That's the conclusion of study published in the New England Journal of Medicine November 22 that examined the effect of three decades of screening mammography on breast-cancer incidence.

The reason: “despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer,” noted Archie Bleyer, MD, of the Oregon Health and Science University, Portland, and the University of Texas Medicine School at Houston, TX, and H. Gilbert Welch, MD, MPH, of the Dartmouth Institute for Health Policy and Clinical Practice, Hanover NJ.

The conundrum: “although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers.”

The authors examined Surveillance Epidemiology and End Results (SEER) data to detect trends from 1976 through 2008 in the incidence of early-stage breast cancer (ductal carcinoma in situ and localized disease) and late-stage breast cancer (regional and distant disease) among women 40 years of age or older.

Drs. Bleyer and Welch found that since screening mammograph was introduced in the United States, the number of cases of early-stage breast cancer detected annually has doubled, from 112 to 234 per 100,000 women, or an absolute increase of 122 cases per 100,000 women.

“Concomitantly, the rate at which women present with late-stage cancer has decreased by 8%, from 102 to 94 cases per 100,000 women—an absolute decrease of 8 cases per 100,000 women. With the assumption of a constant underlying disease burden, only 8 of the 122 additional early-stage cancers diagnosed were expected to progress to advanced disease.”

Therefore, they estimated that “breast cancer was overdiagnosed (i.e., tumors were detected on screening that would never have led to clinical symptoms) in 1.3 million U.S. women in the past 30 years. We estimated that in 2008, breast cancer was overdiagnosed in more than 70,000 women; this accounted for 31% of all breast cancers diagnosed.”

“Our study raises serious questions about the value of screening mammography,” they write. “It clarifies that the benefit of mortality reduction is probably smaller, and the harm of overdiagnosis probably larger, than has been previously recognized. And although no one can say with certainty which women have cancers that are overdiagnosed, there is certainty about what happens to them: they undergo surgery, radiation therapy, hormonal therapy for 5 years or more, chemotherapy, or (usually) a combination of these treatments for abnormalities that otherwise would not have caused illness.”

They concluded by noting that screening proponents “should provide women with data from a randomized screening trial that reflects improvements in current therapy and includes strategies to mitigate overdiagnosis in the intervention group. Women should recognize that our study does not answer the question ‘Should I be screened for breast cancer?' However, they can rest assured that the question has more than one right answer.”


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