Sinonasal melanoma represents the most common mucosal site of melanoma in the head and neck, although cutaneous melanomas are more common by a factor of at least 10-20. It is notable (together with mucosal melanoma arising in other parts of the head and neck) for a poor prognosis and unique staging system.
Epidemiology
Sinonasal mucosal melanoma is a rare disease (< 1% of all melanoma) and detailed epidemiology is not available; it appears to occur most commonly in older adults with no difference seen in gender. It makes up a larger proportion of melanoma diagnoses in blacks.
Aetiology and Pathogenesis
No specific cause is known; smoking and formeldahyde exposure may be important.
Natural History
The tumour is locally invasive and also spreads through lymphatics to regional nodes and distantly to brain, bone, lung and liver.
Tumour/Normal Tissue Features
Macroscopic
Tumours are typically ulcerated with variable level of pigmentation
Microscopic
Cells may have a variety of appearances, with spindle, epithelioid, plasmatoid and rhabdoid appearances described. Cytoplasm is typically eosinophilic and nuclear/cytoplasmic ratio is high. The cells are polymorphic and mitotic figures are common. Unique findings in melanoma may be the presence of melanin pigment within the cytoplasm.
Immunohistochemistry
Immunohistochemistry is particularly important when melanin granules are not present. Staining for vimentin, S100 and melan-A is common. Staining for cytokeratins, CD79, neuroendocrine and neuron specific enolase is negative.
Staging
A variant of the TNM system is used to stage sinonasal mucosal melanoma, which reflects its universally poor prognosis. The same system is used for melanoma of the oral cavity or other head and neck sites.
T Stage
Note that T1 and T2 disease do not exist for sinonasal melanoma
T3: Confined to mucosa
T4a: Invades deep soft tissue, cartilage, bone or skin
T4b: Invades brain, dura, cranial nerves, carotid artery, prevertebral space or mediastinum
N stage
N1: Regional lymph node metastases
M Stage
M1: Distant metastases
Final Stage
| Stage | T | N | M |
|---|---|---|---|
| III | T3 | N0 | M0 |
| IVA | T4a T3-4a |
N0 N1 |
M0 |
| IVB | T4b | Nany | M0 |
| IVC | Tany | Nany | M1 |
