Lifestyle gets blame for 70% to 90% of all cancers

Katie Hill, MarketWatch

Do most people who get cancer simply have bad luck? Or is cancer something they might be able to prevent? Two new studies suggest the latter.

A study published online Friday in the Journal of the American Medical Association Oncology found that between 40 - 70% of cancer cases could be prevented if we changed our lifestyles by doing things like staying at a healthy weight, quitting smoking, reducing alcohol consumption and getting 2 ½ hours of exercise a week. “A large proportion of cancers are due to environmental factors and can be prevented by lifestyle modification,” the authors concluded.

Another study, whose results were recently published in Nature, revealed that it is mostly environmental and external factors like smoking, drinking, diet, getting too much sun and exposure to toxic chemicals that cause cancer, rather than intrinsic factors like random cell mutations.

Intrinsic factors accounted for just 10% to 30% of people’s lifetime risk of getting cancer, while extrinsic risks accounted for 70% to 90% for most common cancer types, the study showed. “Cancer risk is heavily influenced by extrinsic factors,” the study researchers, who work at Stony Brook University in New York, concluded.

That’s good news for many, as it means that cancer might be more avoidable — through changes in our lifestyles — than we previously thought. “Environmental factors play an important role in cancer incidence and they are modifiable through lifestyle changes and/or vaccinations,” the researchers write in Nature. Or as the researchers in JAMA Oncology put it: “A substantial cancer burden may be prevented through lifestyle modification.”

Many experts cheered this finding. “There’s no question what’s at stake here,” John Potter, a doctor who studies cancer at the Fred Hutchinson Cancer Research Center, told Nature. “This informs whether or not we expend energy on prevention.” The authors of the study published in the Journal of the American Medical Association Oncology noted that “prevention should remain a priority for cancer control.”

These conclusions do fly in the face of other cancer research.

A report in the journal Science published earlier in 2015 concluded just the opposite: that roughly two-thirds of cancers were caused by intrinsic factors. (These findings came to be known as the “bad luck” hypothesis.)

But the Stony Brook researchers concluded that the incidence of cancer is too high for that to be true. “The rates of mutation accumulation by intrinsic processes are not sufficient to account for the observed cancer risks,” they write in the study published in Nature.

(This story has been updated with new research.)