Bad luck in cancer

The analysis, published in the journal Science, says genetic mutations that randomly crop up as our stem cells divide are “the major contributors to cancer overall, often more important than either hereditary or external environmental factors.”

The researchers, from the Johns Hopkins University School of Medicine in Baltimore, analyzed published scientific papers to identify the number of stem cells, and the rate of stem-cell division, among 31 tissue types, though not for breast and prostate tissue, which they excluded from the analysis. Then they compared the total number of lifetime stem-cell divisions in each tissue against a person’s lifetime risk of developing cancer in that tissue in the U.S.

The correlation between these parameters suggests that two-thirds of the difference in cancer risk among various tissue types can be blamed on random, or “stochastic,” mutations in DNA occurring during stem-cell division, and only one-third on hereditary or environmental factors like smoking, the researchers conclude. “Thus, the stochastic effects of DNA replication appear to be the major contributor to cancer in humans,” they wrote.

Consumers shouldn’t take this to mean they can continue smoking, drinking and tanning without consequence, said one of the paper’s authors, Cristian Tomasetti.

“Absolutely not. I really want to make sure that is not the message,” said Dr. Tomasetti, an assistant professor of oncology at Johns Hopkins. Cancers of the lung, skin and other tissues are clearly tied to lifestyle factors such as smoking and sun exposure, and people need to remain vigilant about quitting or curbing these behaviors, he said.

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