Melanocytes in malignant ameloblastoma.

An unusual case of malignant ameloblastoma which transformed a pre-existing benign lesion in the maxilla of a 63-year-old Japanese female is reported. In addition to the characteristic histopathological features of less-differentiated malignant ameloblastoma, dendritic-shaped cells containing various amounts of melanin pigment were distributed in the tumor nests invading bone and soft tissue around the maxillary antrum, and some tumor cells containing melanin granules in their cytoplasm were also noted. Neither melanocytes nor melanin pigments were seen within the stroma. Although no firm conclusion of the possible histogenesis of melanocytes in the present case could be drawn, this is the first case of odontogenic epithelial tumor with melanocytosis.