Users of chewing tobacco are most likely to develop cancer at the site where the hold the chew, though this information is anecdotal, and I do not believe that a published study exists. This does not mean that they do not develop oral cancer in other locations; they do, including base of tongue. They are not free from other systemic problems that tobacco in general causes either. As a side note, cancers located at the base of the tongue are still considered oral cavity cancers.