Could most fast food, like mcdonalds and jack n box cause cancer?

I don't think so: Others here will disagree. Everything causes everything if you perform an inept retrospective study. This kind of food has many objectionable features and greatly speeds the process of getting fat, which is linked to a few cancers (famously endometrial). Studies of diet and cancer are so contradictory and perplexing that i've decided that there's little there. Eat sensibly and exercise.