Mine was on the side of my tongue. It started out as leukoplakia, not a canker sore, but it did go through stages where it started to heal and then got worse... I don't think it turned into cancer until it got to the point where it stopped getting better and only worse. I am not sure how long you have been dealing with your sore, but as I mentioned I had mine for a very long time before it turned to cancer. If I would have gotten it checked out sooner, I imagine they could have identified in the biopsy that it was precancerous and removed it. So don't fret too much, if it is something it sounds like you are being proactive and catching it before it becomes anything serious! By the time I finally had someone check it out, they were able to diagnose me on the spot.