Not only mouth cancer. The juice does sometimes get swallowed.
I used to work in a clubhouse and my ex was sports therapist for Cubs minor league when they were in Midland Texas. About half of them chewed the stuff. It was used by high school baseball players too, in the 70s. I knew a 30 year old chewer died from stomach cancer. He started chewing in high school. Everyone agreed it was the baccy.