Most cancer cases down to bad luck, study shows

Most cases of cancer are the result of sheer bad luck rather than unhealthy lifestyles, diet or even inherited genes, research suggests.

Random mutations that occur in DNA when cells divide are responsible for two thirds of adult cancers across a wide range of tissues, a study has shown. The remaining third are linked to environmental factors or defective genes, it found.

But the scientists warn that poor lifestyle can add to the “bad luck factor”.

The researchers analysed published data on the number of divisions of self-renewing stem cells that occur in an average lifetime in 31 different tissues. These results were compared with the lifetime incidence of cancer in the same tissues.

A strong correlation was seen between a particular tissue’s stem cell division rate and its likelihood of developing cancer.

The more often cells divide, the more likely it is that letters of their genetic code will become jumbled, leading to an increased cancer risk.

The study, published in Science, found that random mutations due to stem cell division could explain about 65% of cancer incidence.

Prof Bert Vogelstein, from Johns Hopkins University School of Medicine, said: “All cancers are caused by a combination of bad luck, the environment, and heredity, and we’ve created a model that may help quantify how much of these three factors contribute to cancer development.

“This study shows that you can add to your risk of getting cancers by smoking or other poor lifestyle factors. However, many forms of cancer are due largely to the bad luck of acquiring a mutation in a cancer driver gene regardless of lifestyle and heredity factors. The best way to eradicate these cancers will be through early detection, when they are still curable by surgery.”

“Bad luck” mutations that occur when a chemical letter in DNA is wrongly swapped for another during cell replication largely explained 22 of the 31 cancer types studied. The other nine had incidence rates higher than predicted by bad luck, presumably due to the influence of environmental or inherited factors.

People who live a long life despite exposure to cancer-causing agents such as tob-acco are not so much blessed with “good genes” as good luck, said the professor.

He pointed out that large intestine tissue underwent four times more stem cell divisions than small intestine tissue. And colon cancer was much more prevalent than small intestine cancer.

In mice, the situation was reversed, with the colon undergoing fewer stem cell divisions and being less prone to cancer than the small intestine.

Co-author Dr Cristian Tomasetti said: “If two thirds of cancer incidence across tissues is explained by random DNA mutations ... then changing our lifestyle and habits will be a huge help in preventing certain cancers, but this may not be as effective for a variety of others,.

“We should focus more resources on finding ways to detect such cancers at early, curable stages.”


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