Hi,
Just thought I would jump in here for a second. The mention of constant irritation or trauma..."...was irritated by a tooth or something else." Any persistant or constant trauma/irrotation to tissue puts that tissue in a constant state of healing and regeneration. This process is not always perfect and can deliver a new mutant (cancerous) cell. Anyone who experiences constant irritation or trauma to any spot in their mouth should have the causative agent removed/repaired. This is another reason why regular dental examinations are important.
Cheers,
Mike