Recent theories about the causes of cancer have held that most cancers are caused by internal factors, the result of inevitable mistakes in the human body rather than anything environmental. This would seem to imply that whether or not a person develops cancer is entirely out of his or her control; what that person does in terms of lifestyle choices is irrelevant. And yet the latest high-profile study has strongly challenged this. It estimates that between 70 and 90 per cent of the most widespread cancers have extrinsic causes, such as ultraviolet radiation, pollution and stress. If this study is to be believed, then whether or not you develop some cancers is no longer just something you can blame on your biology, but is to a significant extent within your own control.