MULTIFOCAL AMELANOTIC MELANOMA OF THE HEAD AND NECK: A CHALLENGING CASE

Abstract

Introduction Primary malignant melanoma evolves from melanocytic precursors via the formation of intermediate lesion of varying stability. Less than 1% of all malignant melanomas arise in the head and neck area, the anterior maxilla and alveolar mucosa being the most frequently affected sites. Males and females are equally affected, with an age range between adolescence and senescence. The prognosis is usually poor, with a 5-years survival rate of 30-35% and a median survival of 36 months. Several cases of primary malignant melanoma of the head and the neck area have been reported in the literature but in most cases no clear evidence was shown whether such lesions were primary or metastatic in origin. Case Report We present a case of malignant melanoma in a 50-years old male, who complained for a rapidly growing maxillary nodular lesion, involving the ethmoid sinus and the orbital base. Histopathological intraoperative examination revealed a poorly differentiated malignancy, with spindle-shaped cells showing prominent nucleoli. Subsequent immunohistochemical stains highlighted pan-CK (dot-like) and S100 protein positivity but HMB-45 and melan-A were negative, supporting the diagnosis of malignant melanoma. The tumour was treated by en-block resection with mapping-margins and additional histopathological examination showed an intra-mucosal hyper-melanotic lesion, consistent with an acral lentiginous-type melanoma, which was considered the primary neoplastic focus. Conclusions Primary malignant melanomas in the oral cavity are rare and usually asymtomatic at early stages, thus leading to delayed diagnosis. This must rely upon accurate histopathological and extensive immunohistochemical evaluation as the morphological features often are misleading or non-specific. It is worth to emphasise that melanocyte-specific antigens (Melan-A and HMB-45) frequently are negative in such neoplasm and unexpected cytokeratin positivity may occur, which may result in an inappropriate diagnosis.