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Melanoma 9.4.1

Definition, Epidemiology, Pattern of Growth

Melanoma is composed by a proliferation of me-lanocytes, which derive from the neural crest and subsequently migrate into the skin and mucosal surfaces with an ectodermal origin (Ramos et al. 1990; Manolidis and Donald 1997; Lund et al. 1999; Pandey et al. 1999). Malignant melanoma is usually divided in two categories (cutaneous and mucosal), which, despite a common cytological derivation, differ for biologic behavior. Mucosal melanoma, which is more aggressive, is more rarely observed than the cutaneous counterpart (BatsaKis et al. 1998; PateL et al. 2002b; Medina et al. 2003). In the head and neck region, sinonasal tract and oral cavity are the most frequently involved areas (Medina et al. 2003). Sinonasal malignant melanoma is quite an uncommon observation, accounting for less than 1% of all melanomas and for 2-8% of all the malignancies of the nose and paranasal sinuses (Trapp et al. 1987; Kingdom and Kaplan 1995; Lund et al. 1999). It is more frequent in Caucasians and it usually occurs in patients around the age of 50 or older, even though, in a small rate (10-20%), also younger people may be affected (Rinaldo et al. 2001; Patel et al. 2002b). The most frequent sites of origin of sinonasal malignant melanoma are the nasal septum, the lateral nasal wall, the middle and inferior turbinates (Lund 1993; Manolidis and Donald 1997; Medina et al. 2003). Nevertheless, also paranasal sinuses, in particular maxillary and ethmoid, nasal vestibule and floor of the nasal cavity may be affected (Lund 1993). Localization into the sinonasal tract may also occur as a result of an ocular melanoma invading the sino-nasal tract or of a metastatic spreading from distant sites (Trapp et al. 1987; Patel et al. 2002b). The great majority of patients present with a tumor confined to the primary site, albeit locally advanced (Stage I); far uncommon is the observation at diagnosis of regional (Stage II) or distant metastases (Stage III) (Manolidis and Donald 1997; Patel et al. 2002b). Due to the large size of the lesion at presentation, to the possible presence of multiple neoplastic foci and amelanotic areas (Manolidis and Donald 1997; Lund et al. 1999), the real site of origin and the extent of the lesion are sometimes difficult to assess.

Differential diagnosis is usually with olfactory neuroblastoma, some non-Hodgkin lymphomas, plasmacytoma, Ewing's sarcoma, rhabdomyosar-coma, small cell undifferentiated carcinoma; in the cases without typical histological features, diagnosis may be supported by the immunohistochemical profile (i.e., positivity for S-100 protein, vimentin, and for HMB-45) (Stern and Guillamondegui 1991; Lund et al. 1999; Rinaldo et al. 2001).

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