Jan Peter Kosters and Peter Gotzsche of the Nordic Cochrane Centre in Copenhagen said that the practice may be doing more harm than good, since it led to almost twice as many biopsies that turned up no cancer in women who performed the self-exams, compared to women who didn't do the exams.

The review, published in The Cochrane Library, said two large studies of 388,535 women in Russia and China included in the review, women who used self-breast exams had 3,406 biopsies, compared with 1,856 biopsies in the group that didn't do the exams -- while there was no significant difference in breast cancer deaths between the two groups.

The review is an updated version of a 2003 review of studies, which came to a similar conclusion.

The study authors recognize that some women will want to continue with breast self-exams and women should always "seek medical advice if they detect any change in their breasts that might be breast cancer," Kosters said.