10:57pm Saturday 11 July 2020

Recent Study Should Not Change Mammography Guidelines

By Media Staff  

Colin Begg, Chairman of the Department of Epidemiology and Biostatistics Colin Begg, Chairman of the Department of Epidemiology and Biostatistics

The long-running Canadian study contends that annual screening in women aged 40 to 59 does not lower breast cancer death rates. But experts such as Larry Norton, Memorial Sloan Kettering’s Deputy Physician-in-Chief for Breast Cancer Programs, caution women not to be swayed by the headlines. They say the study has critical weaknesses that invalidate its conclusions and that regular mammography screening continues to be recommended for women in this age group.

“This is further follow-up of a flawed study,” Dr. Norton says. “There are no new data here, so it should not influence any changes in screening recommendations.”

The initial Canadian National Breast Screening Study (CNBSS), which began in 1980, was strongly criticized for two reasons. First, the mammograms performed were judged by outside experts to be of extremely poor quality, and the skills of the imaging technologists were deemed inadequate. Second, the subjects used for the study were not properly randomized into two groups of equal risk for comparison.

Colin Begg, who heads Memorial Sloan Kettering’s Department of Epidemiology & Biostatistics, says the Canadian study has always been an outlier. “It conflicts with all the other large randomized trials conducted a generation or more ago, which showed that mammograms lead to a notable reduction in breast cancer mortality,” he explains.

Study is ‘Flawed and Misleading’

Carol Lee, a diagnostic radiologist at Memorial Sloan Kettering who also chairs the Communications Committee of the Breast Imaging Commission of the American College of Radiology, says, “It is not surprising that the update didn’t show a benefit from screening, as the original report did not.”

The American College of Radiology and the Society of Breast Imaging also called the study “incredibly flawed and misleading.” The organizations released a joint statement saying, “The results of this BMJ study, and others resulting from the CNBSS trial, should not be used to create breast cancer screening policy, as this would place a great many women at increased risk of dying unnecessarily from breast cancer.”

The authors of the BMJ study suggest that annual screening mammograms can lead to “overdiagnosis” of breast cancer, causing women to receive treatments such as surgery for early-stage breast cancers that never would have progressed. But Memorial Sloan Kettering experts assert that it is impossible to determine whether a breast cancer will become dangerous and that fears of overdiagnosis are misplaced.

“Women contemplating screening for breast cancer are overwhelmingly concerned about dying from breast cancer, not the various side effects of screening,” Dr. Begg says.

So what should women do? Bottom line: Doctors at Memorial Sloan Kettering agree that annual mammograms starting at age 40 save lives and decrease the likelihood that women will die of breast cancer by at least 25 to 30 percent. 

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