Breast cancer screenings resulted in a substantial rise in early breast tumors and lesions detected, but didn’t reduce the numbers of advanced cancers diagnosed and likely led to excessive overtreatment, a study of screenings in Denmark reported.
In fact, researchers suggested that one in every three invasive tumors and cases of ductal carcinoma in situ (DCIS) lesions found represented an overdiagnosis, defined as treatment given that exposes a patient to more harm than benefit because the tumor or lesion was not likely to advance during that person’s lifetime.
“These findings support that screening has not accomplished the promise of a reduction in invasive therapy or disease-specific mortality,” the researchers wrote in the study, “Breast Cancer Screening in Denmark A Cohort Study of Tumor Size and Overdiagnosis,” published in Annals of Internal Medicine.
Effective breast cancer screening aims to detect early stage cancer and to reduce the incidence of advanced tumors, but excessive treatment stemming from overdiagnosis is a concern.
Using data from the Danish Breast Cancer Group (DBCG) and the Danish Cancer Registry (DCR), Karsten Juhl Jørgensen, MD, with the Nordic Cochrane Centre in Copenhagen, Denmark, and colleagues examined how cancer screenings offered to women affected the incidence of advanced breast cancer, and the rates of overdiagnosis.
The database included all Danish women, ages 35 to 84, in areas with screening programs or not, who were diagnosed with a breast cancer — advanced or early — from 1980 to 2010.
To determine the screenings’ impact on advanced cancers, researchers compared the incidence of advanced and nonadvanced cancers or lesions diagnosed in areas with and without screening programs. To estimate overdiagnosis, they compared the incidence of advance and nonadvanced cancers reported in women ages 50 to 84 in these two areas, and then compared numbers of nonadvanced tumors reported in screening and nonscreening areas among women broken into age groups: 35–49, 50–69, and 70–84.
Results showed that breast cancer screening with mammography was not statistically associated with a lower incidence of advanced tumors.
Likewise, in 2010, overdiagnosed cases were found in 271 breast tumors and 179 DCIS lesions (an overdiagnosis rate of 24.4% and 14.7%, respectively), the researchers reported. Among women younger than 35 in different regions for that year, they found 711 invasive tumors and 180 cases of DCIS to be overdiagnosed (a rate of 48.3% and 38.6%, respectively).
In an accompanying editorial, Otis Brawley, chief medical officer of the American Cancer Society, said the findings indicate that the benefits of breast cancer screenings programs are more limited than thought. “Considering all small breast cancer lesions to be deadly aggressive cancer is the pathology equivalent of racial profiling,” he said, according to a press release. “This does not mean that screening should be abandoned, but we should try to recognize its limitations, use it in the most effective way possible, and try to improve it.”
Brawley added that focus should instead be placed on preventing breast cancer through exercise, diet, and weight control.
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