Random DNA mutations largely responsible for two thirds of adult cancers but poor lifestyle can add to 'bad luck factor', says study. Most cases of cancer are largely the result of bad luck rather than unhealthy lifestyles, diet or inherited genes, new research suggests.
DNA mutations were mostly to blame for 22 of 31 cancer types that Johns Hopkins researchers studied, including leukemia, pancreatic, ovarian and bone cancer.
It's unfortunately a matter of having bad luck, they said.
"When someone gets cancer, immediately people want to know why," said oncologist Dr. Bert Vogelstein of the Johns Hopkins University School of Medicine. "They like to believe there's a reason. And the real reason in many cases is not because you didn't behave well or were exposed to some bad environmental influence, it's just because that person was unlucky. It's losing the lottery."
The remaining third are linked to environmental factors or defective inherited genes. But the scientists warn that poor lifestyle can add to the "bad luck factor" involved in cancer.
The researchers analyzed 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.
Overall, the study found that random mutations due to stem cell division could largely explain around 65% of cancer incidence.
Professor Bert Vogelstein, from Johns Hopkins University School of Medicine in the US, 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.
Their research is published in the journal Science. Meanwhile, falling smoking rates and better cancer prevention, detection and treatment methods have led to a 22% drop in cancer deaths since 1991. That's more than 1.5 million American lives saved.
The overall rate of cancer incidence decreased from approximately 215 out of every 100,000 people in 1991 to about 169 out of every 100,000 people in 2011.
Rebecca Siegel and her colleagues wrote in CA: A Cancer Journal for Clinicians that a higher reduction in deaths can happen "by applying existing cancer control knowledge across all segments of the population, with an emphasis on those in the lowest socioeconomic bracket and other disadvantaged populations."
"The large geographic variation in cancer death rates and trends reflects differences in risk factor patterns, such as smoking and obesity, as well as disparities in the national distribution of poverty and access to health care, which have increased over time," the researchers wrote.
They envisioned leukemia and cancers of the brain and nervous system as the most diagnosed in children this coming year.