Plain old bad luck plays a major role in determining who gets cancer, according to researchers who found that two-thirds of cancer incidence of various types can be blamed on random mutations and not heredity or risky habits such as smoking.

The researchers said on Thursday that random DNA mutations accumulating in parts of the body during ordinary cell division are the prime culprits behind many cancer types.

The researchers looked at 31 types of cancer and found that 22 types could be explained largely by these random mutations — essentially biological bad luck. The 22 types included leukemia and pancreatic, bone, testicular, ovarian and brain cancer.

The other nine types, including colorectal cancer, skin cancer known as basal cell carcinoma and smoking-related lung cancer, were more heavily influenced by heredity and environmental factors such as risky behavior or exposure to carcinogens. (The study did not cover all cancer types.)

Overall, the researchers attributed 65 percent of cancer incidence to random mutations in genes that can drive cancer growth.

“When someone gets cancer, immediately people want to know why,” said oncologist Bert Vogelstein of the Johns Hopkins University School of Medicine in Baltimore. He conducted the study, published in the journal Science, with Johns Hopkins biomathematician Cristian Tomasetti.

“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.”

Tomasetti said harmful mutations occur for “no particular reason other than randomness” as the body’s master cells, called stem cells, divide in various tissues.

Tomasetti said the study indicates that changing one’s lifestyle and habits such as smoking to avoid cancer risks may help prevent certain cancers, but it may not be as effective for others.

“Thus, we should focus more research and resources on finding ways to detect such cancers at early, curable stages,” Tomasetti added.

The researchers charted the cumulative number of lifetime divisions in the stem cells of a given tissue — for example, lungs or colon — and compared that to the lifetime cancer risk in that tissue.

Generally speaking, tissues that undergo more divisions — thus increasing the probability of random mutations — were more prone to tumors.

— Reuters