WASHINGTON - Plain old bad luck plays a major role in determining who gets cancer and who does not, say researchers who found that two-thirds of cancer incidence of various types can be blamed on random mutations rather than heredity or smoking.
The researchers said that random DNA mutations accumulating in various parts of the body during ordinary cell division are the prime culprits behind many cancer types.
They looked at 31 cancer types and found that 22 of them, including leukaemia and pancreatic, bone, testicular, ovarian and brain cancer, could be explained largely by these random mutations - essentially biological bad luck.
The other nine types, including colorectal cancer, skin cancer and smoking-related lung cancer, were more heavily influenced by heredity and environmental factors such as risky behaviour or exposure to carcinogens.
Overall, the researchers attributed 65 per cent 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, who conducted the study published in the journal Science yesterday with Johns Hopkins bio-mathematician 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."
The study did not cover breast cancer, the most common cancer in women, or prostate cancer, the second most common in men.
Dr Tomasetti said the study indicates changing one's lifestyle and habits may help prevent some cancers, but not others.
"Thus, we should focus more research and resources on finding ways to detect such cancers at early, curable stages," he said.
Adjunct Associate Professor Goh Boon Cher from the Cancer Science Institute of Singapore agrees with the findings.
"There are two types of genetic mutations linked to cancer: one type that you inherit and the other type that just happens.
"The type you inherit is very rare, and occurs in about 5 per cent of common cancers, including breast and colorectal cancer."
He noted that people can still reduce their risk of some cancers. Excessive alcohol drinking, for instance, is linked to liver cancer.
REUTERS, AGENCE FRANCE-PRESSE
Additional reporting by Feng Zengkun