Two-thirds of adult cancers largely due to bad luck, study suggests

Lifestyle choices and genetics are big risk factors for certain cancers, but a new study concludes that the majority of cancer incidence is due mostly to bad luck when our cells divide.

The study comes from scientists at the Johns Hopkins Kimmel Cancer Center who created a statistical model to measure the proportion of cancer cases that are caused mainly by random DNA mutations during stem cell division.

By their calculations, two-thirds of adult cancer incidents can be explained by bad luck when stem cells divide.

All cancers are caused by a combination of bad luck, the environment and heredity, says lead researcher Dr. Bert Vogelstein, a professor of oncology at the Johns Hopkins University School of Medicine.

"Weve created a model that may help quantify how much of these three factors contribute to cancer development, he said in a statement.

Cancer occurs when stem cells in tissues make random mistakes, or mutations, during the replication process in cell division. The more that these mutations accumulate, the higher the risk that cells will begin to grow, unchecked, into tumours.

But Vogelstein says it's never been clearly understood how much of a contribution these random mistakes made to cancer incidence, compared to genetic inheritance, lifestyle, or environmental factors.

So they focused on 31 tissue types, looking at the number of stem cell divisions in each cancer. They then compared these rates with lifetime cancer risk among the same cancer types in the American population.

Significantly, they did not include breast cancer and prostate cancer in their study, even though these are two of the most commonly diagnosed cancers among adults. The researchers explained that they could not find reliable stem cell division rates on these cancer types.

Of the 31 cancer types they did look at, they found that 22 could be largely explained by the bad luck factor of random DNA mutations during cell division.

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Two-thirds of adult cancers largely due to bad luck, study suggests

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