Cancer Sore, the other name for which is aphthous ulcers is mainly caused due to some of the painful sores in the mouth. It occurs in form of a small classic lesion. The sore looks oval or round in shape and it occurs along the erythematous boarder. They can be found in the mucous membranes of the mouth. However, if only the condition turns severe you have to look for apt treatment for the purpose. The Cancer Sore can take place at the time of adolescence and young adulthood. When you grow old there are lesser chances of this disease to occur.