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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 that the death rates from breast cancer and from all causes were the same in women who got mammograms and those who did not. Also, 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 chemotherapy, surgery or radiation.
The study, published Tuesday in The British Medical Journal, 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 findings will not lead to any immediate change in guidelines for mammography. An editorial accompanying the study said that earlier studies that found mammograms helped women were done before the routine use of drugs like tamoxifen that sharply reduced the breast-cancer death rate. Also, many studies did not use the gold-standard methods of the clinical trial, randomly assigning women to be screened or not.
The New York Times