ORAL MELANOACANTHOMA ASSOCIATED WITH PSEUDOMELANOCYTIC NESTS: AN IMMUNOHISTOCHEMICAL STUDY

Oral melanoacanthoma is an uncommon pigmented lesion of the oral mucosa characterized by the presence of acanthosis and dendritic pigment-laden melanocytes located in the prickle cell layer of the epithelium. Pseudomelanocytic nests (PNs) represent cellular aggregates of keratinocytes, macrophages, and melanocytes, usually located in close relationship with lichenoid inflammation, which if not recognized can be misdiagnosed as melanoma. A 41-year-old white woman was referred presenting a pigmented gingival lesion located between the left maxillary central and lateral incisors with 1 year of evolution. After excisional biopsy, microscopy showed typical melanoacanthoma associated with PNs. PNs and dendritic melanocytes were evidenced by Fontana-Masson stain. Immunohistochemistry revealed positivity for AE1/AE3, CD68, and CD163 in PNs, while HMB-45 and Melan-A highlighted dendritic melanocytes. SOX-10 positivity was observed in few melanocytes in basal location. To our knowledge, this is the first report of oral melanoacanthoma associated with PNs. FAPESP (2016/11419-0 and 2017/02502-4).