Bad genes and poor lifestyle choices aren’t the only reasons some people get cancer. A Johns Hopkins Medicine research study attributes most cancer cases to plain old bad luck.
“All cancers are caused by a combination or 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 study author Bert Vogelstein, a professor of oncology at 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.”
The study, found in the Jan. 2 edition of the journal “Science,” states that two-thirds of cancers – or 22 types – are more strongly linked to random gene mutations, or “bad luck,” than others.
Scientists examined the frequency of stem cell division in 31 different types of tissue to determine if the number of divisions could lead to more DNA mutations. They excluded breast and prostate tissues – areas in which cancer is most common – as they were unable to find reliable data on the typical stem cell division rate in these regions.
“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,” Vogelstein said.
For instance, colon tissue stem cells divide four times more than those in small intestine tissue in humans. Colon cancer is also more common than small intestinal cancer.
These new findings, however, aren’t meant to suggest that individuals should continue harmful lifestyle habits and not expect any consequences, said Cristian Tomasetti, a co-author of the study.
“Absolutely not,” said Tomasetti, an assistant professor of oncology at Johns Hopkins. “I really want to make sure that this is not the message.
The remaining one-third of cancers are more heavily influenced by inherited genes and environmental factors. Smoking and prolonged sun exposure, for instance, are linked to lung and skin cancer, respectively.
Although scientists have long known that random mutations that occur during cell division contribute to cancers, Johns Hopkins researchers wanted to quantify its role.
Researchers said they expect the study will change how people think about cancer risk factors. They also believe it could change how cancer studies are funded, with a greater emphasis on finding means to detect “bad luck” cancers at earlier, curable stages.
Habibul Ahsan, a professor of epidemiology, medicine and genetics at University of Chicago Medical Center, said the research was intriguing but weakened because breast and prostate cancers were not included. Additionally, he said there needs to be more research that examines why stem cells in different tissues divide at varying rates. Both Ahsan and the researchers said these differences could be affected by environmental or inherited factors.
(With reports from Al Jazeera, CNN, The Guardian and Wall Street Journal)
