Most Cancers Stem From Avoidable Things: Study

Medically Reviewed by Brunilda Nazario, MD on December 17, 2015
From the WebMD Archives

Dec. 17, 2015 -- Most cases of cancer are due to things some people can avoid, rather than to chance or genetics, a new study in the journal Nature suggests.

The researchers in this study suggest that between 70% and 90% of the most common cancers are caused by things in the environment, like toxic chemicals, radiation, and carcinogens like tobacco smoke.

The study takes on an argument sparked in another journal. Earlier this year, research in Science proposed that genetic abnormalities produced when stem cells divide are largely responsible for whether cancer develops or not. This gave rise to the assumption that a large number of cancers were beyond our control to prevent -- a concept that's been boiled down to the “'bad luck”' theory of cancer risk.

In the new study, doctors from the Stony Brook Cancer Center in New York looked at whether cancer risk rose when people moved from low-cancer-risk areas to areas of high risk, among other things. They found that changing the environment raised the chances of getting the disease.

If most cancers were based solely on genetic abnormalities during stem cell division, then the rates of cancer would not change when people made that move; they would stay the same. Instead, the increase in cancer rates points to something in the environment or external factors as the cause of this rise, the researchers say.

Second Opinion

"Even if someone is exposed to important external risk factors, of course it isn’t certain that they will develop a cancer -- chance is always involved," says Kevin McConway, professor of applied statistics at The Open University.

“It is important to realize that these results do not tell us anything about the absolute risks of any given cancer,” says Paul Pharoah, professor of cancer epidemiology at the University of Cambridge.

"But," McConway says, "this study demonstrates again that we have to look well beyond pure chance and luck to understand and protect against cancers."

"For many common types of cancer, this study concludes ... roughly speaking, that 70% to 90% [of the cancers] would not occur if we could magic away all the risk factors. But this percentage varies between different types of cancer, and in some cancers, it is much smaller, so that in those cases, the external risk factors seem much less important.

"So I don’t think these authors are really claiming that 70% to 90% of all cancers are caused by external risk factors. But they do provide pretty convincing evidence that external factors play a major role in many cancers, including some of the most common,” he says.