Yearly mammograms in middle-age women do not reduce breast cancer deaths — these tests are essentially as good as physical examination alone, according to a new 25-year study from Canada.

The study, which included nearly 90,000 women ages 40 to 59, is the latest to question the value of routine mammography. The researchers found the same number of women died of breast cancer over 25 years, regardless of whether they underwent yearly mammograms or not.

Mammography is performed routinely to screen women for breast cancer, with the goal of early diagnosis. But it is highly debated whether this screening saves lives. In some cases, early detection does not necessarily mean the cancer can be cured, and in some others, treatments work even if cancer is discovered at later stages. [6 Foods That May Affect Breast Cancer Risk]

It is also controversial whether the potential benefits of mammograms outweigh the harm done by overdiagnosis and overtreatment. The new study found that about 22 percent of breast cancers detected by mammograms were what researchers call over-diagnosed, meaning the mammograms revealed tumors that didn't cause disease symptoms, and would not have reduced a woman’s life span if left undetected.

The new findings suggest that "the rationale for screening by mammography should be urgently reassessed by policy makers," the researchers wrote in their study published today (Feb. 11) in the British Medical Journal (BMJ).

"The majority of breast cancers are detectable by mammography, but whether or not this is beneficial has now become very controversial," said study researcher Dr. Anthony Miller, professor emeritus at the University of Toronto.

The studies that had suggested the likely role of screening in reducing breast cancer deaths were performed before modern treatments became available, Miller said. "If you're able to cure cancers by treatment, no matter what stage they're at, there isn't any role for screening. So as the treatment improves, the contribution of screening gets less and less."

Still, it is important for women who are suspicious about something in the breast, a possible lump or distortion, to consult with a doctor. "That is the time when mammography could indeed be very informative as a diagnostic tool," Miller said.

In an accompanying editorial, Dr. Mette Kalager, a breast cancer surgeon and former head of Norwegian Breast Cancer Screening, wrote that the study's findings do not support screening women under age 60. However, changing the policies may not be an easy task, because governments, research funders and physicians may have vested interests, she said.

The breast cancer screening guidelines differ among countries and even organizations. The U.S. Preventive Services Task Force advises women ages 50 to 74 to get mammograms every two years, while the American Cancer Society recommends yearly screening, starting at age 40.

In the study, half of the women had yearly mammograms, along with yearly physical breast examinations, for five years. The other half received only physical examinations and usual care.

After 20 years, 3,250 women in the mammography group and 3,133 in the control group had been diagnosed with breast cancer; 500 women in the mammography group and 505 women in the control group had died of breast cancer.

The results also suggested that one of every 424 women who underwent mammograms in the study was falsely diagnosed as having breast cancer, according to the study.

The study included only women under 60 years old, but it is possible that the findings would apply to older women as well, Miller said.

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