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Mammography associated with overdiagnosis of breast cancer

Breast cancer screening resulted in a substantial overdiagnosis in Denmark, with approximately one in three women being treated unnecessarily, according to recent findings published in Annals of Internal Medicine.

“Effective breast cancer screening should reduce the incidence of advanced tumors,” Karsten Juhl Jørgensen, MD, DrMedSci, from the Nordic Cochrane Centre in Copenhagen, Denmark, and colleagues wrote. “Screening mammography detects many small tumors that would not have become clinically evident in the remaining lifetime without screening (overdiagnosis). Whether screening reduces the incidence of advanced tumors has important therapeutic implications. Overdiagnosed lesions may be unnecessarily treated with surgery, chemotherapy, and radiation, which subjects women to the harms of therapy without benefit.”

Jørgensen and colleagues evaluated the relationship between screening and the size of detected tumors, and estimated overdiagnosis. They performed a cohort study of Danish women aged 35 and 84 years who were diagnosed with invasive breast cancer using biennial mammography between 1980 to 2010. Data from organized breast cancer screening programs in Denmark for women aged 50 to 69 years at various times throughout the early- to mid-1990’s were analyzed.

Breast cancer tumors in screened and unscreened women were measured and documented as either advanced (>20 mm) or nonadvanced (20 mm). Overdiagnosis trends were estimated using two approaches in both screening and nonscreening areas. The first approach compared the incidence of advanced tumors among women aged 50 to 84 years, while the second approach compared the incidence of nonadvanced tumors among women aged 35 to 49, 50 to 69, and 70 to 84 years.

Results indicated that screening did not lower the incidence of advanced tumors. There was an increase in the incidence of nonadvanced tumors in the screening period as opposed to the prescreening period (incidence rate ratio, 1.49; 95% CI, 1.43-1.54). The first estimation approach showed that in 2010, there was an overdiagnosis of 271 invasive breast cancer tumors and 179 ductal carcinoma in situ (DCIS) lesions at a rate of 24.4% including DCIS and 14.7% excluding DCIS. The second estimation approach showed that in 2010, there was an overdiagnosis of 711 invasive tumors and 180 cases of DCIS at a rate of 48.3% including DCIS and 38.6% excluding DCIS.

“Seventeen years of organized breast screening in Denmark has not measurably reduced the incidence of advanced tumors but has markedly increased the incidence of nonadvanced tumors and DCIS,” Jørgensen and colleagues wrote. “Further, we found evidence for substantial overdiagnosis.”

“These findings raise questions about whether screening provides the promised benefits of reduced breast cancer mortality, less invasive treatment, and reduced disease burden,” they concluded.

In an accompanying editorial, Otis Brawley, MD, MACP, chief medical officer of the American Cancer Society, wrote that while overdiagnosis of breast cancer is often difficult to accept as it “challenges the values of screening” and suggests that the “benefits of screening have been overstated,” the overdiagnosis is real.

“In many respects, considering all small breast lesions to be deadly and aggressive types of cancer is the pathologic equivalent of racial profiling,” he wrote.

However, he emphasized that screening should not be neglected.

“We must carefully examine screening, realize its limitations, maximize its effectiveness, and try to improve it,” Brawley wrote. “In addition, we must examine all elements of breast cancer control (to include prevention) and evaluate how they are best used.”

He suggests that beyond screening, breast cancer can be controlled or prevented through diet, weight control and exercise. – by Alaina Tedesco

Disclosure: The authors do not report relevant financial disclosures.