Speaking as a cancer survivor who made active choices and participated fully, and am now officially in remission – and know many others who were just as vigilant but did not make it – I’d say your distinction is nonexistent.
There are genetic markers that make one more susceptible to addiction. How is that any different than having genetic markers for cancer?
And what about people who “choose” to work in environments that later turn out to be cancer-causing? Are they responsible for their affliction, too?