LONDON: Two-thirds of the world’s cancer cases are a direct result of bad luck rather than faulty lifestyle or defective DNA.

In first such analysis, scientists say that cancers are driven by random mistakes in cell division which are completely outside human control. Scientists from the Johns Hopkins Kimmel Cancer Centre have created a statistical model that measures the proportion of cancer incidence, across many tissue types, caused mainly by random mutations that occur when stem cells divide.

They came to their conclusions by searching the scientific literature for information on the cumulative total number of divisions of stem cells among 31 tissue types during an average individual’s lifetime.

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By their measure, two-thirds of adult cancer incidence across tissues can be explained primarily by “bad luck” when these random mutations occur in genes that can drive cancer growth, while the remaining are due to environmental factors and inherited genes.

“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,” says Bert Vogelstein, the Clayton Professor of Oncology at the Johns Hopkins University School of Medicine.

They found that 22 cancer types could be largely explained by the “bad luck” factor of random DNA mutations during cell division.

The other nine cancer types had incidences higher than predicted by “bad luck” and were presumably due to a combination of bad luck plus environmental or inherited factors.

“We found the types of cancer that had higher risk than predicted by the number of stem cell divisions were precisely the ones you’d expect, including lung cancer, which is linked to smoking; skin cancer, linked to sun exposure and forms of cancers associated with here­ditary syndromes,” said Vogelstein.

“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,” added Vogelstein.

A Lancet study earlier had said that cancer deaths accou­nted for six per cent of deaths across all ages, but among the 30-69 years age group the rate rose to eight per cent.

“Cancer-free longevity in people exposed to cancer-causing agents, such as toba­cco, is often attributed to their ‘good genes’, but the truth is that most of them simply had good luck,” said Vogelstein, who cautioned that poor lifestyles could add to the bad luck factor in the development of cancer.

Published in Dawn, January 3rd, 2015

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