In general, base of tongue cancers start out as a hard spot, that if you are doing a screening, you can feel with your finger as you pass it over the base of the tongue. As the cancer matures, it becomes a pronounced bump in most all of the cases. In some cases the cancer starts growing inward, versus outward, and that is referred to as involution of the mass. These tend to be caught later, as the patient does not have the sensation that swallowing is getting harder to accomplish, which drives them to and ENT or their doctor with a complaint.