Smoke-Screening

My past couple of posts have included lots of praising of others—the speakers who’ve been presenting sessions at the Medical Evidence Boot Camp this week—and I hope you’re not sick the praises, because today was no different. Barnett (Barry) Kramer, MD, MPH, Director of the Division of Cancer Prevention at the National Cancer Institute completely pulled the curtain back on cancer screening, with evidence and insights that revealed screening to be rife with smokescreens.

I hope to write about this area of cancer care more extensively some time, but a few snapshots for now. First, a simple understanding about how screening can improve survival rates without changing anything at all. Many readers might know about all this already, but – it’s called lead time bias. The simplified explanation that Barry Kramer gave today was this: say 100 people are diagnosed with a type of cancer that leads to death four years later for all of them, without exception. What is the 5-year survival rate? 0. But now say you detect the cancer earlier – say, two years earlier. Those 100 people are still living just as long. But now the 5-year survival rate is 100%. Nothing has changed. The cancer hasn’t been treated better, the people haven’t actually lived any longer. They’ve only lived for a longer amount of time with cancer.

Dr. Kramer spent a few hours discussing screening with us, and to be clear, he’s not “anti-screening.” And in fact he talked about which screening tests he thinks are good, or worth considering, and for which data are emerging that will help define the potential usefulness. But he raised several red flags of caution. Selection bias is another problem – the population of people who get screened may not represent the larger population of people who get a particular type of cancer overall. (By analogy: Why do Volvos have such a low accident rate? Because people who tend to drive safely think, “I’m a safe driver! I’m going to buy the safe car. And they don’t get into accidents because they drive safely, and so Volvos keep on having the lowest rate of accidents.) Then there is a length bias in screening, which has to do with the fact that some cancers are very slow growing. This is oversimplified, but basically, at any given point there are more people with slow-growing cancers than there are with fast-growing cancers.

The slow-growing ones may not be harmful at all—many will not grow or will disappear on their own, or will grow so slowly that the individual will die of something else before the cancer does any harm—but more of them are detected by screening because more of them exist in the world. Rapidly progressing cancers, which are the ones that tend to be more dangerous, can miss detection via screening because they grow quickly; a tumor can emerge and grow between screenings. Length bias leads to overdiagnosis, because tumors that never would have caused harm end up being subjected to treatment that can leave a person worse off than they were or ever would have been. As Dr. Kramer put it (in my paraphrase…) treating people who are healthy rarely leads to anything good.

There was so much more to think about, but one of the big messages that finally started sinking in today is that there are things in healthcare that do more harm than good. We all know this, right? It’s something I’ve heard again and again and again. Even in the course of these few days, we’ve been hearing the question: does the benefit outweigh the risk? But by the end of today it was finally taking hold of my little brain: there are interventions that do more harm than good. That’s something to just stop and think about. It’s like we have a default setting that believes interventions are good, and so even when we hear the words “this may do more harm than good,” the message is sort of watered down by this underlying adherence to the belief that no, no, no, really there must be some good in it, just maybe not that much good. But that just isn’t true. I know screening is a hugely contentious issue, and personally I find it very difficult to believe that certain screening tests are not helpful, and could be, or maybe will most definitely be, harmful. And yet.

Early detection can lead to unnecessary treatments which can have severe, negative consequences on a person’s health and well being. Just the fact of being labeled as a “cancer patient” can have terrible fallout, especially considering that a person may never have had any negative effects on his/her health from cancer in their entire lifetime.

Again, this is not to say that all screening is bad, or that it should not be done. But clearly there is a lot more room for thoughtful discussion, and for having the courage to sometimes just say no.

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