Immunohistochemical features of multifocal melanoacanthoma in the hard palate: a case report

Based on the differential diagnosis of melanoma, a punch biopsy (4 mm in diameter) was performed. The material was fixed in 10% formalin, embedded in paraffin, and stained with hematoxylin-eosin or submitted to immunohistochemical analysis. Immunohistochemistry using antibodies against protein S-100, melan-A, HMB-45, MCM-2, MCM-5, Ki-67 and geminin was performed. Immunohistochemical analysis revealed strong cytoplasmic immunoreactivity of dendritic melanocytes for proteinS-100, HMB-45 and melan-A.Positive staining for proliferative markers (MCM-2, MCM-5, Ki-67) was only observed in basal and suprabasal epithelial cells, confirming the reactive etiology of the lesion. The diagnosis was oral Melanoacanthoma (MA).The patient has been followed up for 30 months and shows no clinical alterations. MA should be included in the differential diagnosis of pigmented lesions of the oral cavity.In an attempt to better define the melanoepithelioma types 1 and 2 described by Bloch (1937), Mishima & Pinkus (1960) were the first to use the term melanoacanthoma (MA) [1]. According to these authors, MA corresponds to Bloch’s melanoepithelioma type 1, a rare variant of pigmented seborrheic keratosis characterized by the proliferation of melanocytes and keratinocytes in the lower layers of the epithelium [2].The first report of oral MA was published by Schneider and coworkers (1981) [3]. Since then, MA has been described in the oral mucosa as a solitary lesion or, occasionally, as multiple lesions [2]. MA mainly affects dark skinned patients and grows rapidly, showing a plane or slightly raised appearance and a brown to black color. The differential diagnosis includes oral nevi, amalgam tattoos, and melanomas [4-8]. Histologically, MA is characterized by the proliferation of sparse melanocytes throughout the epithelium and epithelial spongiosis. An increase in the number of melanocytes in the basal layer and the presence of a chronic submucosal inflammatory infiltrate containing eosinoph