Caramel coloring produced using ammonia and sulfites , like in Pepsi and Coke, produce 2-methylimidazole (2-MI) and 4-methylimidazole (4-MI). Both, 2-MI and 4-MI are implicated in promoting cancer in lungs, liver, and thyroid of lab rats and mice, including hypertrophy of the pituitary gland.
Uses big doses per kilogram of body weight, but the doses recommended max per day of 4-MI is 16 mcg for humans in California. 12 ounces of soda provides well over 100 mcg of 4-MI. Did I not mention all other foods that people eat that use the caramel food coloring as a bonus to that total? It's the ammonia and sulfite produced caramel coloring only that is implicated. I'm quite aware of the other nasties in soda, especially mercury contamination.