This older report suggested that two thirds of cancer was because of random mutation, rather than genetic predisposition or lifestyle.
Here's an example of the confusing way that older study was reported: http://www.theguardian.com/society/2015/jan/02/two-thirds-ad...
> Two-thirds of adult cancers, say the researchers from the Johns Hopkins Kimmel Cancer Center in the United States, are caused by random mutation in the tissue cells during the ordinary process of stem cell division. In the other third, our genetic inheritance and lifestyles are the main factors.
> The scientists have created a mathematical model which, they say, shows it is wrong to assume that there are such things as “good genes” that may prevent us getting cancer even though we smoke, drink heavily and carry excessive weight.
This new study disputes that, and says that normal random mutation only accounts for 10% to 30% of cancer, and the rest is because of lifestyle or genetic predisposition.
From a public health point of view that's pretty important. Stop smoking, and control how much alcohol you drink, continue to be important public health messages to reduce the incidence of cancer.