A black blood blister on the tongue is not necessarily cancer. It could be a blood blister from a bite, or it could be a hemangioma. Tongue cancer is characterized by the growth of a cauliflower-like swelling, or a long-term ulcer that does not heal. Generally, mouth ulcers can heal on their own in 7-10 days, but if the ulcer cannot heal repeatedly for more than 1 month, it is necessary to see a hospital in time. Among tongue cancers, malignant tumors of the tip of the tongue have a better prognosis because the blood supply is not as good. However, the prognosis of tongue root cancer is especially bad, because the blood supply of tongue root is very good and it is easy to have lymph node metastasis and distant metastasis at an early stage. Therefore, if you find repeated bad ulcers in the mouth or tongue, you must go to a regular specialized hospital in time to avoid adverse consequences.