The New Uncertainty about Mammograms


“I’d like to be tested for every kind of cancer.”

All primary care doctors have heard this request. Our answer is an explanation that we can’t. Understanding this explanation is important before we get to the most recent study about mammograms.

We don’t test for all kinds of cancers for an important reason. The outcome of most cancers don’t depend on when they are diagnosed. This may come as a surprise to many, since we’ve all heard the message of the importance of early diagnosis. But that message only applies to a handful of cancers. Diagnosing colon cancer early definitely saves lives, hence the value of screening colonoscopies. Early diagnosis of cervical cancer is also beneficial, hence Pap tests. But many cancers do not fit this pattern. Take leukemia for instance. Some leukemias are curable; others are not. When they’re diagnosed makes little difference. So testing everyone for leukemia wouldn’t save any lives.

This problem is compounded in cancers that are very-slow growing and occur mostly in older people. These cancers, if undetected, may never harm the patient, and the patient could live a normal lifespan and die of an entirely unrelated problem. Detecting these cancers early doesn’t help anyone. That’s called over-diagnosis – diagnosing a disease that would have never caused harm. (That’s a major problem with prostate cancer screening and is why ” target=”_blank”>I reviewed the evidence in a post back then.) The U.S. Preventive Services Task Force (USPSTF) combined the data of all the randomized studies of mammograms and calculated that on average 1 life is saved from breast cancer for every 377 women in their 60s who undergo mammograms. For women in their 50s the benefit is smaller (i.e. more women must have mammograms to save one life) and for women in their 40s the benefit is smaller still. Because of the very small benefit to women in their 40s the USPSTF recommended against routine mammograms in this age range. (I disagreed in my post.) And they recommended mammograms every two years for women between the ages of 50 and 74.

This month the British Medical Journal published ” target=”_blank”>Vast Study Casts Doubts on Value of Mammograms (New York Times)
” target=”_blank”>Cancer screening expert to radiologists: Stop lying about mammograms (Los Angeles Times)
” target=”_blank”>Mammography Screening (The Medical Letter blog)
” target=”_blank”>New Mammogram Recommendations Betray Women, Doctors and Science (my post in 2009 reviewing the evidence on mammography)

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Anything you read on the web should be used to supplement, not replace, your doctor’s advice.  Anything that I write is no exception.  I’m a doctor, but I’m not your doctor.

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