One of the largest and most meticulous studies of mammography ever done, involving 90,000 women and lasting a quarter-century, has added powerful new doubts about the value of the screening test for women of any age.
It found the death rates from breast cancer and from all causes were the same in women who got mammograms and those who did not. And the screening had harms, too: One out of five cancers found with mammography and treated was not a threat to the woman’s health and did not need treatment, such as chemotherapy, surgery or radiation.
The study, published in The British Medical Journal, is one of the few rigorous evaluations of mammograms conducted in the modern era of more effective breast cancer treatments. It randomly assigned Canadian women to have regular mammograms and breast exams by trained nurses or to have breast exams alone.
Researchers sought to determine whether there was any advantage to finding breast cancers when they were too small to feel. The answer was no, the researchers report.
The study seems likely to lead to an even deeper polarization between those who believe that regular mammography saves lives – including many breast cancer advocates and patients – and a growing number of researchers who say the evidence is lacking or, at the very least, murky.
“It will make women uncomfortable, and they should be uncomfortable,” said Dr. Russell P. Harris, a screening expert and professor of medicine at the University of North Carolina. “The decision to have a mammogram should not be a slam dunk.”
The findings will not lead to any immediate change in guidelines for mammography, and many advocates and experts will almost certainly dispute the idea that mammograms are, on balance, useless – or even harmful.
But an editorial accompanying the new study said earlier studies finding mammograms helped women were done before the routine use of drugs, such as tamoxifen, that sharply reduced the breast cancer death rate. In addition, many studies did not use the gold-standard methods of the clinical trial, randomly assigning women to be screened or not.