All the carbohydrates will be coated with Acrylamide or burnt to a crisp. Acrylamide is believed to be a carcinogen (Acrylamide is converted to a compound called glycidamide , which causes mutations in and damage to DNA) and shown to be in animal models.

Once you're frying, roasting, and grilling things at this temperature you are increasing cancer risk completely unrelated to any cooking materials involved. That's true of french-fries, bread, steaks and a zillion other things. It's why they're tasty (see Malliard reaction).

I certainly consider cast iron relatively safe, but it's polymerized unsaturated oil is likely to leach acrylamide and associated chemicals. It's just that compared to the food you're eating it's not relevant.