Released: 30-Dec-2014 1:50 PM EST Embargo expired: 1-Jan-2015 2:00 PM EST Source Newsroom: Johns Hopkins Medicine Contact Information
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Newswise Scientists from the Johns Hopkins Kimmel Cancer Center 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 weve created a model that may help quantify how much of these three factors contribute to cancer development, says Bert Vogelstein, M.D., the Clayton Professor of Oncology at the Johns Hopkins University School of Medicine, co-director of the Ludwig Center at Johns Hopkins and an investigator at the Howard Hughes Medical Institute.
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, adds Vogelstein, who cautions that poor lifestyles can add to the bad luck factor in the development of cancer.
The implications of their model range from altering public perception about cancer risk factors to the funding of cancer research, they say. 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, says biomathematician Cristian Tomasetti, Ph.D., an assistant professor of oncology at the Johns Hopkins University School of Medicine and Bloomberg School of Public Health. We should focus more resources on finding ways to detect such cancers at early, curable stages, he adds.
In a report on the statistical findings, published Jan. 2 in Science, Tomasetti and Vogelstein say 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 individuals lifetime. Stem cells self-renew, thus repopulating cells that die off in a specific organ.
It was well-known, Vogelstein notes, 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. The actual contribution of these random mistakes to cancer incidence, in comparison to the contribution of hereditary or environmental factors, was not previously known, says Vogelstein.
To sort out the role of such random mutations in cancer risk, the Johns Hopkins scientists charted the number of stem cell divisions in 31 tissues and compared these rates with the lifetime risks of cancer in the same tissues among Americans. From this so-called data scatterplot, Tomasetti and Vogelstein determined the correlation between the total number of stem cell divisions and cancer risk to be 0.804. Mathematically, the closer this value is to one, the more stem cell divisions and cancer risk are correlated.
Our study shows, in general, that a change in the number of stem cell divisions in a tissue type is highly correlated with a change in the incidence of cancer in that same tissue, says Vogelstein. One example, he says, is in colon tissue, which undergoes four times more stem cell divisions than small intestine tissue in humans. Likewise, colon cancer is much more prevalent than small intestinal cancer.
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'Bad Luck' of Random Mutations Plays Predominant Role in Cancer, Study Shows
