美国国家公共电台 NPR Cancer Is Partly Caused By Bad Luck, Study Finds

KELLY MCEVERS, HOST:

There are a lot of reasons why people get cancer. Sometimes it's exposure to something toxic 1 like smoke. Sometimes it's just bad genes 3. New research finds most of the genetic 4 mutations that lead to cancer crop up naturally, and they're unavoidable. NPR's Richard Harris reports.

RICHARD HARRIS, BYLINE 5: First the backstory - two years ago, Bert Vogelstein and Cristian Tomasetti at Johns Hopkins University started controversy 6 by suggesting that many cancers are unavoidable. Critics said that was undercutting the message that many cancers are preventable. So when these scientists had new results to report, Vogelstein made that point absolutely clear.

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BERT VOGELSTEIN: We all agree that 40 percent of cancers are preventable. The question is, what about the other cancers that aren't known to be preventable?

HARRIS: Speaking at a news conference, Dr. Vogelstein and his colleague explained how they have now refined that question.

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VOGELSTEIN: Every time a perfectly 7 normal cell divides, it makes several mistakes, mutations.

HARRIS: Most of the time, those mutations are in unimportant bits of DNA 8. That's good luck.

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VOGELSTEIN: But occasionally they occur in a cancer driver gene 2. That's bad luck.

HARRIS: After two or three of these driver genes get mutated in the same cell, the cell can turn cancerous. In their new paper in Science, the researchers set out to quantify how often these mutations are random 9 errors that result from cell division, how often they're caused by nasty chemicals like tobacco smoke and how often they're inherited.

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VOGELSTEIN: Sixty-six percent of the total mutations are random, about 29 percent due to the environment and the remaining 5 percent due to heredity.

HARRIS: These numbers depend on the type of cancer. Lung cancer is largely triggered by environmental causes - smoking - while the vast majority of childhood cancer is a result of these bad luck mutations. Right now, Vogelstein says parents who focus on environment and heredity are likely to think they are somehow responsible for their child's disease - not so.

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VOGELSTEIN: They need to understand that these cancers would have occurred no matter what they did. We don't need to add guilt 10 to an already tragic 11 situation.

HARRIS: Of course people can reduce their risk of preventable cancer by avoiding tobacco and eating well. As for the mutations that occur spontaneously...

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VOGELSTEIN: Now, what can people do - nothing - right now, nothing. This is a question for research.

HARRIS: In fact the paper raises many questions. Martin Novak is a biologist and mathematician 12 at Harvard.

MARTIN NOVAK: The question is super fascinating. So the question is really, how much of human cancer is caused by bad luck? How much is caused by bad things that we do? The question is super fascinating.

HARRIS: He says the new findings are provoking discussion among cancer scientists, and that's all for the good.

NOVAK: How exactly we can actually answer these questions? It is very unclear to me whether we have the tools in hand right now.

HARRIS: So you don't expect this paper to put to rest the controversy that the first one stirred up.

NOVAK: No, I think it will raise an even bigger controversy.

HARRIS: One of the big sticking point is that mutations, while necessary, aren't the whole story. Dr. Graham Colditz at Washington University in St. Louis isn't convinced that hazards have been neatly 13 sorted into the categories of heredity, environment and unavoidable mutations.

GRAHAM COLDITZ: How these interplay with each other I think is still potentially more complex.

HARRIS: Vogelstein and Tomasson (ph) are prepared to argue these matters with their colleagues, and on one point at least they do agree. While mutations are necessary for cancer, they don't entirely 14 explain why some mutated cells eventually become aggressive, deadly cancers and others don't. Richard Harris, NPR News.

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