A Canadian study that many experts say has major flaws has revived debate about the value of mammograms. The research suggests that these screening X-rays do not lower the risk of dying of breast cancer while finding many tumors that do not need treatment.
The study gives longer follow-up on nearly 90,000 women who had annual breast exams by a nurse to check for lumps plus a mammogram, or the nurse’s breast exam alone. After more than two decades, breast cancer death rates were similar in the two groups, suggesting little benefit from mammograms.
The study did not compare mammograms to no screening at all, as most other research on this topic has. Many groups have not endorsed breast exams for screening because of limited evidence that they save lives.
Critics of the Canadian study also say it used outdated equipment and poor methods that made mammograms look unfairly ineffective. The study was published Wednesday in the British journal BMJ.
The Canadian study has long been the most pessimistic on the value of mammograms. It initially reported that after five years of screening, 666 cancers were found among women given mammograms plus breast exams compared with 524 cancers among those given the exams alone.
After 25 years of follow-up, about 500 in each group died, suggesting mammograms were not saving lives. The similarity in the death rates suggests that the 142 “extra” cancers caught by mammograms represent overdiagnosis — tumors not destined to prove fatal, study leaders concluded.
The work was immediately criticized. The American College of Radiology and Society of Breast Imaging called it “an incredibly misleading analysis based on the deeply flawed and widely discredited” study.
