One of the largest and most meticulous studies of mammography ever done, involving 90,000 women and lasting a quarter-century, has added new doubts about the value of the screening test for women of any age.
It found that 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 — one out of five cancers found with mammography and treated was not a threat to the woman's health and did not need treatment like chemotherapy, surgery or radiation.
The study, published Tuesday 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.
In the United States, about 37 million mammograms are performed annually.