Nov. 20th, 2009

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Doing my part to echo reason in the skeptical blogosphere, I’ll make a brief mention of what I’ve read about the new USPSTF guidelines, which you may have heard of. If not, Dr. David Gorski explains and deconstructs. The short version is, a group belonging to (but not setting policy for) the US government has altered its recommendations for mammographic screening to

  1. not screen women aged 40–49 anymore (rather, wait until 50)
  2. screen once every two years, instead of annually

Naturally, a lot of people misunderstand this and some of the less reasonable among them start crying about misogynism and the Obama administration’s death panels. These people miss a lot of obvious points.

  • These are screening guidelines. They have nothing to do with recommendations for symptomatic women (examining them is not screening, but diagnosis). It also does not apply to women with known risk factors. It’s a change in how they suggest screening of asymptomatic women should happen.

  • The group was not set up by the Obama administration. The US authorities do not condone these guidelines. In fact, most groups do not, though if Dr. Gorski is right, a gradual shift in this general direction may happen over time. Either way, the USPSTF just makes recommendations; they have no power to dictate policy.

  • The tricky one: The guidelines actually make a lot of sense. Excessive screening does more harm than good.

It may sound bizarre that more cancer screening could be harmful, but it’s true. Apart from discomfort and angst caused by false positive diagnoses, there’s very real pain and even small danger in performing biopsies on harmless lumps (even good medical interventions are never completely risk free). And, not all cancers will kill you—a few may spontaneously go away, but much more significantly, a lot of cancers are just so slow-growing that they shouldn’t be on your list of worries. With the average life expectancy around 80, a tumour that will absolutely kill you by your 110th birthday is…really nothing to worry about. You’re more likely to live longer without the harsh regimen of surgery, chemotherapy, and radiation necessary to treat the cancer, even though that same regimen is an absolute life-saver if you have the sort of cancer that would kill you before you’re certainly dead by natural causes.

There are also other factors, such as lead time bias (highly recommended reading). It’s easy to say that If we screen 40-year-olds, most diagnosed cancer patients survive on average 15 years; if we only screen 50-year-olds, we find that our average patient only survives 5 years and think that early screening lets people live longer (15 years versus 5!)…but I’ve just described two scenarios with people dying at age 55; the difference is how long they live with the knowledge that they have cancer. This sort of thing happens, it is significant, and it confounds trials and policy making. Detecting cancers earlier is only helpful if interventions actually turn out to save lives.

I won’t say much further, because this is obviously not my area of expertise, but because a moral panic has sprung up around the internet, I figured I would say something in case you stumble across my blog. If these issues concern you, I highly recommend David Gorski’s write-up, the SkepChick counter to a bad Feministing report, and Orac’s direct deconstruction of the canards and conspiracy theories.

haggholm: (Default)

Your hardware has changed significantly since first install, it informs me, so you have to re-activate Windows. Would you like to do so now?

Sure, I installed some new devices…but they were virtual devices.


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Petter Häggholm

April 2016

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