Doubts about the benefits of mammograms to screen women for breast cancer should be dispelled by a new study conducted by seven major research groups. Mammograms have long been recommended as an effective tool for detecting tiny breast tumours. But four years ago, an analysis published in a British medical journal found so many flaws in studies that purported to show a benefit from mammography that the results were deemed virtually meaningless. Other experts agreed that the evidence was shaky, but mainstream cancer organisations remained convinced that mammograms save lives.

Now comes a study, published in The New England Journal of Medicine that was conducted by research teams including both sceptics about mammograms and believers. The study sought to estimate the relative importance of screening mammograms and powerful new drugs in producing a 24 per cent decline in breast cancer mortality.

The results varied widely. One team found screening responsible for 65 per cent of the decline and drug therapies a mere 35 per cent. Another team gave drugs 72 per cent credit. What seems important is that each team found at least some benefit from mammograms. Women still need to make their own judgments as to whether the usefulness of screening outweighs the risks.