It’s a finding that should relieve the anxiety of people searching for answers to the question “Why me?” when they develop cancer. A study from Johns Hopkins University finds that more than two thirds of the genetic mutations that cause cancer occur at random – the result of chance mistakes in DNA replication that occur when normal cells divide. The idea was to quantify those DNA-copying errors – as opposed to inherited genes and environmental factors like smoking and obesity.

The scientists 32 types of cancer. Overall, they found 66 per cent of the mutations are due to those replication mistakes, but the proportion was different for different cancers. In pancreatic cancer for example, 77 percent of the mutations were random, 18 percent related to factors like smoking, and the remaining 5 percent were caused by heredity.

For Lung cancer, the picture was completely different with 65 percent of all the mutations due mostly to smoking, and 35 percent resulting from DNA copying errors. Inherited factors are not known to play a role.

The researchers say cancer patients who have avoided known risk factors should be comforted by these findings. The bottom line – it’s not their fault!