Nature Medicine | Spoonful of Medicine

Now you see it… now you don’t

New research suggests that mammography, the low dose x-ray procedure that helps doctors diagnose small tumors in the breast, might frequently pick up tumors that will go away on their own. Scientists in Norway tracked two populations of over 100,000 women between the ages of 50 and 64. One group received mammograms every two years while those in the other group had a single mammogram at the end of the six-year study. The incidence of invasive breast cancer (the type of cancer that has spread beyond the milk ducts and into the surrounding tissue) was 22% higher in the frequent screening group. This finding led researchers to speculate that mammograms had detected cancers that would have regressed if the women had received no treatment. Otherwise they would expect the two groups, which had parallel risk factors, to have similar breast cancer incidence.

Without further research, it is unclear how often mammograms detect cancers that spontaneously regress. But if it happens as often as this study suggests, then doctors will have to spend more time thinking about how one can distinguish between a cancer that is likely to regress on its own and one that could progress and threaten a woman’s life. Should women endure surgeries, radiation and chemotherapy for cancers that could potentially disappear with no treatment at all?

If some 20% of cancers picked up in mammograms actually do regress within six years, it seems risky to assume they would disappear forever. Perhaps, in a decade or two, some of these tumors could return more aggressive than ever. Or if these cancers do vanish indefinitely, understanding what prevents them from mustering a full-fledged assault on the body might help scientists develop new treatment strategies.

Undoubtedly, this article raises a host of interesting research questions. But where does the scientist begin? I think we need longer term studies comparing groups of women receiving frequent and infrequent mammograms in order to determine if the incidence rates remain disparate beyond six years. What do you think should be on the agenda for future studies?


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