Oral mucosal melanoma with unusual clinicopathologic features

Oral mucosal melanoma (OMM) is an extremely rare malignancy, accounting for < 0.5% of all melanomas and all oral malignancies. The rarity of OMM, the heterogeneity in clinical and histopathologic appearances, and the paucity of molecular and genetic studies to date have limited our knowledge of the etiopathogenesis of these cancers. A 39-year-old Hispanic male presented for evaluation of a large, pigmented, plaque-like and nodular growth of the maxillary gingival and palatal mucosa. On presentation, a presumptive clinical diagnosis of mucosal melanoma was made, which was confirmed by incisional biopsy with subsequent histopathologic evaluation. Macroscopically, the morphology and highly pigmented nature of the tumor was suggestive of a rarer subtype of melanoma known as animal-type melanoma, also referred to as pigmented epithelioid melanocytoma. However, microscopically, the tumor showed histopathologic features consistent with a high-grade acral (mucosal) lentiginous melanoma with overt cytomorphologic features of malignancy in addition to showing prominent pigment synthesis resembling animal-type melanoma. A detailed search of the literature did not identify a previous report of OMM with prominent pigment synthesis resembling animal-type melanoma. Identification of melanoma subtypes has specific implications for therapeutic approach, and thus their recognition is important to successful patient management.