A black blood blister on the tongue is not necessarily cancer, it could be a blood blister from a bite or a hemangioma. Tongue cancer is characterized by the growth of a cauliflower-like swelling, or long-term ulcers can not heal. Generally, mouth ulcers can heal by themselves in 7-10 days, but if the ulcers can’t be healed repeatedly for more than 1 month, it is necessary to go to the hospital in time. Among tongue cancers, the prognosis of tongue tip malignant tumor is better, because its blood supply is not so good. However, the prognosis of tongue root cancer is particularly bad, because the blood supply of tongue root is very good, and it is easy to develop lymph node metastasis and distant metastasis at an early stage. Therefore, if you find repeated bad ulcers in mouth or tongue, you must go to regular specialized hospitals in time to avoid bad consequences.