Report: Unavoidable typos in DNA help fuel cancer

WASHINGTON — Cancer patients often wonder “why me?” Does their tumor run in the family? Did they try hard enough to avoid risks like smoking, too much sun or a bad diet?

Lifestyle and heredity get the most blame but new research suggests random chance plays a bigger role than people realize: Healthy cells naturally make mistakes when they multiply, unavoidable typos in DNA that can leave new cells carrying cancer-prone genetic mutations.

How big? About twothirds of the mutations that occur in various forms of cancer are due to those random copying errors, researchers at Johns Hopkins University reported Thursday in the journal Science.

Whoa: That doesn’t mean most cases of cancer are due solely to “bad luck.” It takes multiple mutations to turn cells into tumors — and a lot of cancer is preventable, the Hopkins team stressed, if people take proven protective steps.

Thursday’s report is an estimate, based on a math model, that is sure to be hotly debated by scientists who say those unavoidable mistakes of nature play a much smaller role.

But whatever the ultimate number, the research offers a peek at how cancer may begin.

And it should help with the “why me” question from people who have “done everything we know can be done to prevent cancer but they still get it,” said Hopkins’ Dr. Bert Vogelstein, a pioneer in cancer genetics who co-authored the study. “They need to understand that these cancers would have occurred no matter what they did.”

You might inherit some mutations, like flaws in BRCA genes that are infamous for causing aggressive breast and ovarian cancers in certain families.

More commonly, damage is caused by what scientists call environmental factors — the assault on DNA from the world around us and how we live our lives. There’s a long list of risks: Cigarette smoke, UV light from the sun, other forms of radiation, certain hormones or viruses, an unhealthy diet, obesity and lack of exercise.