Clinicopathological study on primary malignant melanoma of the oral mucosa. Part I. Histological features of our nine cases.

Malignant melanoma of the skin is now classified into four major types: 1) lentigo maligna melanoma (LMM), 2) superficial spreading melanoma (SSM), 3) nodular melanoma (NM), 4) acral lentiginous melanoma (ALM). However, classification of melanoma of the oral mucous membrane has not yet been well-documented. We discussed clinico-pathologically our nine oral melanoma cases and the following findings were obtained.1. Eight of nine cases showed three lesion phases clinically; a nodular lesion (A-phase), a plaque lesion (B-phase), and a macular lesion (C-phase).2. Histological examination revealed spindle or epithelioid tumor cells in A-phase, pre-invading tumor cell nests resembling pagetoid tumor nests in B-phase, proliferation of dendritic melanocytes or simple hyperpigmentation along the basal cell layer in C-phase.3. According to the above findings, eight cases were interpreted as ALM, while one case lacking for B-and C-phase was considered as NM.