Junctional nevus of the oral mucosa. Light and electron microscopic observations.

Junctional nevi of the oral mucosa are rare and may be precancerous. A patient who had an enlarging junctional nevus of the labial mucosa with an adjacent lentigo simplex was studied by light and electron microscopy. On the basis of morphologic similarities--dentritic appearance, lack of desmonsomes, proliferative melanin production, and lack of cytoplasmic fibrils--it appears that the nevus cell most likely develops from melanocytes. The reason for the transformation from melanocyte to nevus cell or junctional nevus cell hyperplasia is unknown.