Mouth ulcers are not a precursor to cancer. Mouth ulcers are a disease of the autoimmune system, but it is important to determine if a mouth ulcer is a cancerous ulcer. If the location of the mouth ulcer does not change and it remains in one place for a long time, for more than a month, it is necessary to be alerted and go to the hospital for diagnosis, or even for timely removal and pathological examination. If the mouth ulcer is only recurrent, but the location of the ulcer changes frequently, it is usually called recurrent aphthous ulcer, which itself does not cause cancer and patients can rest assured. However, mouth ulcers are also very troubling to everyone. You can take light salt water gargle and insist on it for more than six months, usually recurrent aphthous ulcers can be cured.