A patient presents with a flat, bluish-gray discoloration on the buccal mucosa that has been present for years. There is no elevation, pain, or associated lymphadenopathy. Which diagnosis is LEAST likely?

A flat, bluish-gray mucosal discoloration is characteristic of an amalgam tattoo, blue nevus, or early mucosal melanoma. A fibroma is a raised, pink or flesh-colored lesion of normal mucosal color — it does not present as a bluish-gray flat lesion. Therefore, fibroma is the least likely diagnosis for a flat bluish-gray discoloration. Amalgam tattoos are the most common cause of focal oral pigmentation. Blue nevi and melanoma must be considered and differentiated, particularly if the lesion is growing or elevated.