According to a series of articles by Parkin et al 2011 published as a supplement of the British Journal of cancer, one third of all cancers are caused by tobacco, unhealthy diet, alcohol, and obesity. About 40% of all cancers are caused by things we mostly have the power to change say the authors. [1]
In a foreword Professor Sir Richard Peto writes that tobacco still remains the most important avoidable cause of cancer, responsible for almost 20% of all cases of cancer