It could be nothing, but during the "Let's cook" scene with Jesse, they show Todd in the full hazmat suit/gas mask get up, and Jesse without one. If indeed they do say Jesse has to cook without the proper safety precautions, six to nine months of inhaling meth fumes will seriously fuck up his body.

Again, maybe it's nothing/not the case, but it would be a "poetic" ending for the character, in that Walt's presence really did end up being a cancer.