We reported the clinicopathological features of primary malignant melanoma of the oral cavity in the Part I and II. In this Part, we studied 20 cases of benign and premalignant pigmented lesion in the oral mucosa. The 20 cases consisted of 1 premalignant and 19 benign (4 pigmented nevi, 12 non-nevoid melanocytic lesions, and 3 others) lesions.
Pigmented nevus was divided into three types; junctional, compound and intramucosal nevus. Non-nevoid melanocytic lesion showed various degree of proliferation of dendritic or clear cell-like melanocytes, hyperpigmentation in the basal cell layer, and phagocytosis of melanin in the connective tissue.
One case of premalignant melanocytic lesion occurring in the lower lip had two phases; the plaque and the macular lesions. The plaque lesion revealed proliferation of atypical melanocytes and small nest formation along the basal cell layer. The macular lesion consisted of mild proliferation of melanocytes having no cellular atypia, and hyperpigmentation in the basal cell layer. According to these findings, the lesion was considered to be precursor of ALM.
Precursor lesion of oral malignant melanoma has not been well documented. We discussed here the potential of malignant transformation of pigmented nevus and non-nevoid melanocytic lesion of the oral mucosa.
