A study has confirmed that about 41 percent of cancers are caused by the environment and lifestyles: http://cmajopen.ca/content/5/3/E540.full
But you don’t need to swim through the technicalities of the paper, as there is a neat summary provided by the authors:
“Background: Estimates of the proportion of cancer cases that can be attributed to modifiable risk factors are not available for Canada and, more specifically, Alberta. The purpose of this study was to estimate the total proportion of cancer cases in Alberta in 2012 that could be attributed to a set of 24 modifiable lifestyle and environmental risk factors.