Breast self-exams, which many doctors recommend despite little evidence of benefit, do women more harm than good, according to new research.

A review of two studies involving nearly 400,000 women in Russia and China found that those who performed self-exams underwent almost twice as many biopsies that did not find tumours as women who did not examine themselves.

(Biopsies are invasive procedures that remove fluid or tissue that is then analyzed for signs of cancer.)

There was no meaningful difference in the two groups' death rates.

The U.S. Preventive Services Task Force, an expert panel that issues the federal government's official advice on preventive medicine, no longer recommends routine breast self-exams.

Both the American and Canadian cancer societies call breast self-exams optional for most women, noting that their benefits are unclear.

The review was published in the July issue of the Cochrane Library.