Author: Daniel Yiu, Foundation Year Doctor, Department of Infectious Diseases, Oxford Foundation School, Frimley Health NHS Trust, Wexham Park Hospital, Slough, Berkshire, United Kingdom. DermNet NZ Editor-in-Chief: Adjunct A/Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. January 2019.
Spindle cell melanoma is a rare histological variant of melanoma characterised by the presence of spindle-shaped melanocytes . On microscopy, it is often mistaken for other skin and soft tissue cancers with spindle cell morphologies.
Desmoplastic melanoma is a variant of spindle cell melanoma where there are varying proportions of spindle cells and desmoplastic cells.
Further studies are needed to clarify clinical manifestations, risk factors, treatment management and prognosis of spindle cell melanoma.
The actual incidence of spindle cell melanoma is unknown. Studies have suggested that between 1 and 14% of melanomas are of the spindle cell variant (including desmoplastic melanoma) [2,3].
Spindle cell melanomas more commonly occur in Caucasian males, affecting men and women at a ratio of 1.6:1 to 1.9:1 respectively. The average age at diagnosis is 50–80 years [1,4].
The exact cause of spindle cell melanoma is unknown. Spindle cell melanoma shares common mutations with conventional (epithelioid) melanoma.
Spindle cell melanoma frequently presents as a non-specific amelanotic (nonpigmented) nodule on the trunk, head, or neck [1,3].
It may also first present as widespread melanoma metastases.
Metastasis is the major complication of spindle cell melanoma. Delays in diagnosis can occur due to its atypical presentation histologically [1–3].
The non-specific features may lead to delays in the diagnosis of spindle cell melanoma, which is often not suspected clinically. The diagnosis is generally made on a biopsy of the lesion but can also be commonly mistaken for another tumour histologically .
A combination of histological clues and immunohistochemistry markers are required to diagnose spindle cell melanoma .
Features of spindle cell melanoma under microscopy include:
Special stains may be used to differentiate spindle cell melanoma from other spindle cell tumours.
Spindle cell melanoma can be easily confused with other spindle cell tumours.
Desmoplastic melanoma was described as a variant of spindle cell melanoma in 1971 . Recent studies suggest that desmoplastic melanoma and spindle cell melanoma represent two distinct types of melanoma, as differences in staining, genetic mutations, and clinical manifestations have been found .
Reed naevus (also called pigmented spindle cell nevus) is a melanocytic naevus with a largely spindle-cell appearance under microscopy. The architecture is symmetrical with good lateral demarcation, epidermal hyperplasia, and uniform nests of cells .
The differentiation of cutaneous clear cell sarcoma from spindle cell melanoma is largely histological, as both may stain positively for S100, HMB45 and Melan-A. Cutaneous clear cell sarcoma tends to show uniform patterns of spindle cell fascicles under microscopy, which are present throughout an entire tumour and encased by fibrous septa. The stroma tends to be hyalinised, sclerotic and reticulated .
Leiomyosarcoma pathology may be indistinguishable morphologically from melanoma.
Treatment of spindle cell melanoma is similar to other forms of melanoma. Surgical excision is the first step in management .
Although the tendency for nodal involvement is low, the majority of spindle cell melanomas present with advanced disease ; worse prognosis is seen in Caucasian males of age > 66 years.
Advanced disease with nodal and distal metastasis is associated with worse outcomes in spindle cell melanoma, as are higher grades, which have been associated to poorer disease-specific survival (DSS) and overall survival (OS) .
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