Most cases of cancer are the result of sheer 'bad luck' rather than just unhealthy lifestyles, diet or even inherited genes, new research suggests.
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.
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 third 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," said Bert Vogelstein, Professor of Oncology at the Johns Hopkins University School of Medicine.
"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 cautions that poor lifestyles can add to the bad luck factor in the development of cancer.
Researchers said the implications of their model range from altering public perception about cancer risk factors to the funding of cancer research.
"If two-thirds of cancer incidence across tissues is explained by random DNA mutations that occur when stem cells divide, 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," said Cristian Tomasetti, an assistant professor of oncology at Johns Hopkins.
Researchers searched 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. Stem cells "self-renew," thus repopulating cells that die off in a specific organ.
It was well-known, Vogelstein noted, that cancer arises when tissue-specific stem cells make random mistakes, or mutations, when one chemical letter in DNA is incorrectly swapped for another during the replication process in cell division. The more these mutations accumulate, the higher the risk that cells will grow unchecked, a hallmark of cancer.
Researchers classified the types of cancers they studied into two groups. They statistically calculated which cancer types had an incidence predicted by the number of stem cell divisions and which had higher incidence.
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 incidents higher than predicted by "bad luck" and were presumably due to a combination of bad luck plus environmental or inherited factors.
The findings appear in the journal Science.