NEW YORK: Going for the annual mammogram may not be entirely helpful, according to a new study.

The study, published on Tuesday in The British Medical Journal, found that death rates from breast cancer and from all causes were the same in women who got mammograms and those who did not.

In fact, there may be drawbacks linked to regular screening. One out of five cancers found with mammography and treated was not a threat to the woman's health and did not need treatment like chemotherapy, surgery or radiation, the New York Times reported, citing the findings. The study, which involved 90,000 women in Canada over a period of 25 years, was one of the largest and most meticulous studies of mammography ever done. It randomly assigned Canadian women to have regular mammograms and breast examinations by trained nurses or to have breast exams alone.

The new study came amid a growing debate between those who believe that regular mammography saves lives, and researchers who say the evidence is lacking.

Click on image above to find out the pros and cons of breast screening.

But no nations except Switzerland have suggested the screening be halted. In a recent report, the Swiss Medical Board advised that no new mammography programmes be started in that country, citing concerns over the effectiveness of such screening.

In Singapore, women aged 40 to 49 are advised to go for a mammogram once a year while women above 50 are encouraged to go for one every two years. In the United States, about 37,000,000 mammograms are performed annually. Nearly three-quarters of women aged 40 and older said they had a mammogram in the past year.

The aim of the latest study was to determine whether there was any advantage to finding breast cancers when they were too small to feel. And the answer was no, according to the researchers who called on policymakers to "urgently reassess" the rationale for screening by mammography.

In an editorial titled "Too Much Mammography" accompanying the study, Dr Mette Kalager, an epidemiologist and screening researcher at the University of Oslo and the Harvard School of Public Health, wrote that other studies had suggested that improved treatment, such as the routine use of drugs like tamoxifen, rather than screening, was the reason for the decline in breast cancer mortality in the past four or five years.

Dr Kalager also compared mammography to prostate-specific antigen, a form of screening for prostate cancer, which is currently not encouraged in Britain and other countries. The findings of the study showed that the absolute harms (over-diagnosis) and benefits (mortality reduction) are not very different between the screening types.

"Nevertheless, the UK National Screening Committee does recommend mammography screening for breast cancer but not prostate-specific antigen screening for prostate cancer," she wrote, adding that "political pressure and beliefs might have a role". "As time goes by, we do indeed need more efficient mechanisms to reconsider priorities and recommendations for mammography screening and other medical interventions," she added.

But the findings of the new study will not lead to any immediate change in guidelines for mammography, said the New York Times. The report quoted Dr Richard C. Wender, chief of cancer control for the American Cancer Society, as saying that combined data from clinical trials of mammography showed it reduces the death rate from breast cancer by at least 15 per cent for women in their 40s, and by at least 20 per cent for older women. He added that while improved treatment has helped lower the breast cancer death rate, so did mammography, through early detection.

Commenting on the Canadian study, Dr Russell P. Harris, a screening expert and professor of medicine at the University of North Carolina, told the New York Times: "It will make women uncomfortable, and they should be uncomfortable. The decision to have a mammogram should not be a slam dunk."