Malignant (cancerous) ulcers tend to have certain characteristics:
1) Large or enlarging
2) Presenting for more than 2 weeks. The lining of the mouth turns over within 2 weeks, so any benign ulcers, cuts, or scrapes should heal within this time.
3) Underlying hard lump. This is known as induration and indicates that there is an increased number of cells in the underlying tissue or an enlarged lymph nodes.
4) One-sided swelling or drooping/slanting of the face, lip or tongue.
5) Swelling of the lymph nodes in the neck
An experienced examiner will be able to advise if an ulcer in your mouth is something to be potentially concerned about.
If there is a concern about a particular ulcer, then the ONLY way to confirm a diagnosis of oral cancer is with a biopsy. A small sample of tissue will be taken from the ulcer and a small portion of normal tissue beside the ulcer. This will be looked at under the microscope to look for cancerous or pre-cancerous cells.