For quite a few years now the conventional wisdom has been that all women over the age of 40 should get a yearly mammogram so that doctors can catch any breast tumors present in the earliest, most treatable stages. But a recently published study challenges that recommendation.

An annual mammogram offers no better reduction in the risk of death from breast cancer than regular self-exams and clinical exams which require no exposure to potentially dangerous radiation, according to the new research.

A team from the University of Toronto found that 22 percent of tumors discovered via mammography were harmless tumors that would not result in symptoms or death.

The authors say that their findings may not be applicable to undeveloped countries, but in technically advanced, developed countries, “our results support the views of some commentators that the rationale for screening by mammography should be urgently reassessed by policy makers.”

Rethinking the need for regular mammograms in those under 60 is likely to be a challenge. Many governments and other institutions which set health policy and fund research — as well as some scientists and physicians — may have “a vested interest” in continuing with well-established practices.

Researchers randomly assigned almost 90,000 women to receive either five annual mammograms or no mammograms during the five-year screening period. The women were followed for 25 years: 180 women in the mammography group and 171 women in the non-mammogram control group died of breast cancer.

Over the entire 30-year study period, 500 women in the mammography group and 505 women in the control group died of breast cancer. The findings for women ages 40-49 and 50-59 were identical. The investigators concluded that the risk of death from breast cancer was the same for both the mammography and non-mammography groups.

In an editorial accompanying the study, Mette Kalager, a medical doctor and researcher at the University of Oslo in Norway, and her colleagues say that although they agree with the findings of the Toronto study, rethinking the need for regular mammograms in those under 60, “is not an easy task, because governments, research funders, scientists, and medical practitioners may have vested interests in continuing activities that are well established.”

Older women who have seen how health policies and practices change over time may also be reluctant to reduce what has been considered the gold standard of breast cancer preventive care.

The study and editorial are published online in BMJ, The British Medical Journal.