Dustin Diamond‘s cancer medical diagnosis has actually been hard for him to handle mentally … and it has him questioning how this took place to him.

The “Saved by the Bell” star’s associate informs TMZ … Dustin’s having a hard time to come to terms with having the kind of lung cancer he has — phase 4 little cell cancer — since it’s typically triggered by smoking cigarettes, and he’s never ever been a cigarette smoker.

So, we’re informed Dustin can’t assist however question if his cancer is the outcome of his regular work travel over the previous twenty years.

The associate states Dustin’s worked all over the nation on movie sets and at funny clubs for meet-and-greets … and in some cases needed to remain in quite doubtful hotels and motels, since there were no other choices.

We’re informed Dustin thinks a few of these areas may have had mold or asbestos … which he might have taken in, triggering his cancer.

As we reported … Dustin simply finished his preliminary of chemo at a Florida healthcare facility, and will begin physical treatment quickly while he waits for the 2nd round of treatment.

We’re informed his physicians have actually not identified what triggered his cancer, however as we reported … he does have a history of it in his household. His mom passed away of breast cancer.