Chronic stress --> enhanced intracellular oxidation --> endogenous mutagenesis --> higher likelihood of developing cancer.
I bet his lifestyle had quite a bit to do with his disease, but bleh, sucks he had to go out that way, and it was a 7-year-long, protracted battle with a cascade of organ failures to boot. The guy had serious balls (and vision, too, I guess) to trudge through something that debilitating to keep heading to work every day.