Junctional nevus of the oral mucosa

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—dendritic appearance, lack of desmosomes, 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.