An extended follow up of the Canadian National Breast Screening Study (CNBSS), published this week in the British Medical Journal, added more fuel for the contentious debate over mammography screening.
Anthony B. Miller, MD, of the University of Toronto, and colleagues reexamined the findings of CNBSS now that study participants had been followed for a mean of 22 years, and found that annual mammography does not reduce breast cancer mortality for women aged 40-59 beyond what is achieved with usual care and physical examination.
The study also found that an excess of invasive breast cancer was observed in the mammography arm, resulting in a rate of overdiagnosis of 22 percent.
Reactions to the study were split, with some touting the strengths of the study and others pointing out flaws in its design. An accompanying editorial from Mette Kalager, MD, of the University of Oslo, Norway, said the strengths of the study included a randomized design, long-term follow up and high compliance.
Kalager compared mammography to the much maligned prostate-specific antigen (PSA) screening test for prostate cancer, saying the two screening tests had similar overdiagnosis rates. Despite this, there is more support for mammography compared to PSA screening.
The American College of Radiology (ACR) and the Society for Breast Imaging (SBI) issued a joint statement critical of the study, calling the CNBSS “deeply flawed and widely discredited.” The statement claimed that experts who have reviewed the CNBSS found the quality of the mammography used to be poor and that the technologists and radiologists involved had no special training in mammography. CNBSS also violated protocol for randomized controlled trials by evaluating patients before randomly assigning them to screening or non-screening arms, according to the statement.
While the ACR and SBI pleaded that the CNBSS not be used to create screening policy, Miller and colleagues wrote that their results “support the views of some commentators that the rationale for screening by mammography should be urgently reassessed by policy makers.”
And at least one set of mammography guidelines may indeed see updates in the near future, as the New York Times reported that the American Cancer Society—which has advocated for yearly mammograms starting at age 40—has convened an expert panel to review all studies on mammography and will issue revised guidelines later this year.
Editor – Health Imaging