A picture shows a white lesion on the floor of the mouth — very white, spongy-appearing, non-ulcerated. What is the MOST likely diagnosis?

White Sponge Nevus (WSN) presents as bilateral, symmetric, folded/spongy white plaques on the buccal mucosa and floor of mouth. It is benign, autosomal dominant, caused by mutations in keratin 4 or 13, and is non-ulcerated. The key distinguishing feature is the 'spongy' white appearance without induration. SCC would present with induration, ulceration, or fixation. Candidiasis is typically wiped off. Leukoplakia is flat, not spongy.