Potential overdiagnosis may be significantly associated with breast cancer screening
Danish researchers assessed screening programs offering biennial mammography for women ages 50 to 69 years to determine trends in the incidence of advanced and nonadvanced breast cancer tumors.
Breast cancer screening was not associated with a reduction in incidence rates of advanced cancer and might represent overdiagnosis of tumors that would not become clinically relevant, according to a Danish cohort study.
To assess the association between screening and the size of detected tumors and to estimate potential overdiagnosis, Danish researchers studied women ages 35 to 84 years from 1980 to 2010. Screening programs offering biennial mammography for women ages 50 to 69 years were assessed to determine trends in the incidence of advanced (>20-mm) and nonadvanced (≤20-mm) breast cancer tumors in screened and nonscreened women.
Two approaches were used to estimate the amount of overdiagnosis. The first compared the incidence of advanced and nonadvanced tumors among women ages 50 to 84 years in screening and nonscreening areas. The second compared the incidence for nonadvanced tumors among women ages 35 to 49, 50 to 69, and 70 to 84 years in screening and nonscreening areas. Study results were published by Annals of Internal Medicine on Jan. 10.
Screening was not associated with lower incidence of advanced tumors, the authors found. Nonadvanced tumor incidence increased in the screening versus prescreening periods (incidence rate ratio, 1.49 [95% CI, 1.43 to 1.54]). The first estimation approach found that 271 invasive breast cancer tumors and 179 ductal carcinoma in situ (DCIS) lesions were overdiagnosed in 2010 (overdiagnosis rate, 24.4% including DCIS and 14.7% excluding DCIS). However, these estimates did not account for the relative decrease in advanced cancer rates, which was similar in screening-eligible and screening-ineligible age groups.
The second approach accounted for regional differences in women younger than the screening age and found that 711 invasive tumors and 180 cases of DCIS were overdiagnosed in 2010 (overdiagnosis rate, 48.3% including DCIS and 38.6% excluding DCIS). Therefore, one in every three breast tumors detected in women ages 50 to 69 years was probably overdiagnosed, the authors wrote.
“Our data show that the introduction of breast cancer screening was not associated with reduced rates of advanced cancer when we accounted for incidence trends in women younger than the screening age,” the authors wrote. “The introduction of breast screening was clearly associated with increased rates of nonadvanced breast tumors and DCIS, which were not compensated for by a decrease in incidence in women no longer invited to screening.”
An editorial by the chief medical officer of the American Cancer Society called for careful examination of breast cancer screening to help determine its limitations, make it as effective as possible, and attempt to improve it. “In addition, we must examine all elements of breast cancer control (to include prevention) and evaluate how they are best used,” he wrote. He called for more emphasis on such preventive measures as diet, weight control, and exercise, as well as chemoprevention in high-risk women.
In addition, he wrote, “Women who are currently diagnosed with breast cancer should continue to be treated based on the current guidelines to prevent confusion. Genomic testing is already helping to determine tumors that warrant intensive therapy versus those that need less aggressive treatment. In the future, genomic profiling will identify some breast tumors that can be carefully observed.”