One-Third of Breast Cancer Patients Overdiagnosed

Cancer screenings do not reduce the incidence of advanced tumors.

One of every 3 women who receive a mammogram resulting in a breast cancer diagnosis is treated unnecessarily, according to a study published in Annals of Internal Medicine.

The investigators sought to assess the association between breast cancer screening and the size of detected tumors, and to estimate overdiagnosis defined as the detection of tumors that would not become clinically relevant.

The cohort study measured trends in the incidence of advanced (>20 mm) and nonadvanced (≤20 mm) breast cancer tumors in screened and nonscreened women in Denmark from 1980 to 2010.

Two approaches were used to estimate the amount of overdiagnosis: comparing the incidence of advance and nonadvanced tumors among women aged 50 to 84 years in screening and nonscreening areas; and comparing the incidence for nonadvanced tumors among women aged 35 to 49 years, 50 to 69 years, and 70 to 84 years in screening and nonscreening areas.

The second approach accounted for regional differences in women younger than the screening age.

The results of the study showed screening was not associated with a lower incidence of advanced tumors, and the incidence of nonadvanced tumors increased in the screening versus prescreening periods (incidence rate ratio, 1.49 [95% CI, 1.43 to 1.54]).

Using the first estimation approach, the investigators found that 271 invasive breast cancer tumors and 179 ductal carcinoma in situ (DCIS) lesions were overdiagnosed in 2010 (overdiagnosis rate of 24.4% [including DCIS] and 14.7% [excluding DCIS]).

The second approach revealed that 711 invasive tumors and 180 cases of DCIS were overdiagnosed in 2010 (overdiagnosis rate of 48.3%) [including DCIS] and 38.6% [excluding DCIS]).

A limitation to the study was that regional differences can complicate interpretation, the authors noted.

The findings indicated that breast cancer screening was not associated with a reduction in advanced cancer incidence. Furthermore, the results suggest the likelihood that 1 of every 3 invasive tumors and cases of DCIS diagnosed in women offered screening represent overdiagnosis.

In an accompanying editorial, Dr Otis Brawley, chief medical officer of the American Cancer Society, wrote that all tumors cannot be treated the same. Some early tumors can turn lethal, while others shrink or stop growing completely. To assume all small breast lesions have the potential to turn deadly is akin to “racial profiling.”

“By treating all the cancers that we see, we are clearly saving some lives,” Brawley told CNN. “But we’re also ‘curing’ some women who don’t need to be cured.”

Overdiagnosis and false positives can cause women with benign growths to undergo biopsies and other additional follow-up testing. These risks have pushed some experts to reevaluate breast cancer screenings overall, CNN reported.

According to the Agency for Healthcare Research and Quality, mammograms are unable to detect all tumors. However, they can reduce the risk of death by 25% to 31% for women aged 40 to 69 years.