Benefit of mammograms even greater than thought

"We saw the actual number of overdiagnosed cases was really very small -- less than 5 percent of the total," Robert Smith, director of cancer screening at the American Cancer Society and one of the study's authors, said in a telephone interview.

Many groups, including the American Cancer Society, have stuck by their long-standing recommendations of a yearly breast exam for women starting at age 40, stressing that the breast X-rays have been proven to save lives by spotting tumors early, when they are most easily treated.

"I think for anybody who was beginning to have their faith shaken in the value of mammography, these data show mammography is quite valuable as a public health approach to reducing deaths from breast cancer," Smith said.

Duffy said he thinks screening women 40 to 54 every 18 months and screening women 55 and older every two years would be a reasonable schedule.

He said the new findings do not speak to the frequency of screening issue, but they do make clear that screening works.

"Everyone must make up their own mind, but certainly from combined results from all the screening trials, mammography in women aged 40-49 does reduce deaths from breast cancer," he said.

Breast cancer is the second-leading cause of cancer death among U.S. women, after lung cancer. It kills 500,000 people globally every year and is diagnosed in close to 1.3 million people around the world.

(Editing by Todd Eastham)

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