To mammogram or not

You may have heard about the new mammogram screening guidelines– from the American Cancer Society– that came out today (every year from 45-55; every two years thereafter).  This led to the best thing I’ve yet read on mamograms– a 538 post from Christie Aschwanden that puts this all in perspective.  Short version: it’s not about science, it’s about what sorts of trade-offs make sense in terms of false positives versus fatal cancers prevented.  Anyway, here’s the key chart:


I found this especially timely as my wife who is 43 recently had her first mammogram.  (I told her to follow the USPSTF guidelines and wait till 50, but hey, it’s her body).  She was called back for a second mammogram, which, of course, led to plenty of anxiety on her part.  Mammograms are more difficult and harder to get right on younger (under 50), denser breasts, so this was not at all surprising, but still a definite psychological cost.  As it turned out she’s actually got some old blocked milk ducts (how about that– it’s been around 4 years since they’ve been used), that looked funny, but she’s fine.  Of course, even if she had needed a biopsy, as you can see above, chances are strong it would have been unnecessary.

Anyway, here’s the key summary:

When weighing the benefits and risks, it’s helpful to look at absolute numbers. In a clinical review published in JAMA Internal Medicine on Tuesday, Karla Kerlikowske, a physician at the University of California, San Francisco, presented some figures: A woman’s lifetime risk of dying from breast cancer is 2.7 percent without screening. Kerlikowske calculates that a woman who follows the new USPSTF guidelines could drop that risk to 2.0 percent, and one who follows the ACS guidelines may reduce the risk a few decimal places more, to between 1.8 and 1.9 percent. To get these benefits, the USPSTF program requires 13 total mammograms in a woman’s lifetime, and the ACS regimen will result in 20 breast X-rays.

In exchange for these risk reductions, 61 percent of women who have annual mammograms and 42 percent of women who have biennial mammograms will be called back at least once for follow-up tests that reveal they do not have cancer, researchers write in an accompanying paper. The anxiety and stress of such a false alarm is the most common harm, but it’s not the only one.

In its own analysis, the USPSTF calculated that if 1,000 women follow its advice and have a mammogram every other year from age 50 to 74, 146 of them will be subjected to unnecessary breast biopsies and 18 of the 1,000 will be diagnosed and treated for a cancer that would have never harmed them (a problem called overdiagnosis and overtreatment). Women who have mammograms more often, as they would under the ACS guidelines, will experience more of these downsides.

And, about those trade-offs:

Underneath the debate about at which age and at what frequency we should urge women to get mammograms, another important question looms: Is it reasonable to recommend a test that will produce false positives for something like half of the people who take it? Is it OK to risk harming hundreds of women in hopes of helping a handful avert a breast cancer death? The ACS and USPSTF have concluded yes, but that’s a value judgment, not a scientific one.

Amid all this conflicting advice, patients have to make their own decisions. After more than 15 years reporting on this issue, I’ve decided to skip mammograms altogether. My No. 1 priority is to remain a healthy person and avoid unnecessary treatments, and opting out of mammographyreduces my risk of becoming a breast cancer patient by one-third. A smart friend of mine has examined the same evidence and come to the opposite conclusion, choosing to follow the ACS guidelines…

What we’re both seeking is assurance and certainty, and those are things that neither choice can guarantee.

Honestly, what I think is most useful is people actually understanding the choices that they are making.  And I think right now, far too few women actually do.

About Steve Greene
Professor of Political Science at NC State

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