Mouth ulcer belongs to oral mucosa disease, and should be listed in oral mucosa department, and biopsy should be performed for mouth ulcer suspected to be cancerous, as follows. 1. If oral ulcers do not heal for a long time, and are accompanied by unclear edge, granular base, tough texture, bleeding, necrosis and other symptoms, it is generally suspected that oral ulcers may be cancerous, and it is necessary to take biopsy to make a clear diagnosis. 2. Usually, it is necessary to register with the oral mucosa department, and under the operation of the oral mucosa doctor, part of the oral ulcer tissues and adjacent normal tissues will be cut out, and then sent to the Department of Pathology for examination. If the above symptoms occur, it is recommended to go to the hospital in time to receive regular treatment as soon as possible.