Pathology of Desmoplastic
Melanoma and Neurotropic
(DM) is a variant of melanoma characterized by the presence of amelanotic
fusiform melanocytes dispersed in a prominent collagenous stroma.
Desmoplastic neurotropic melanoma (DNM) is a neurotropic variant of desmoplastic melanoma.
DM and DNM occurred most often in lentiginous-type melanomas. Lentigo maligna melanoma is associated with DM and DNM
The clinical presentation of DM and DNM
differs from that of other melanomas. These lesions usually occur in
older patients (median age of 61 years, compared with a median age of 46
years for other melanomas.)
These are usually amelanotic lesions.
Most desmoplastic melanomas are variants of lentigo maligna melanoma.
Unlike immature scar tissue, in desmoplastic melanoma there is neurotropism, epidermal proliferation of melanocytes, and S100 protein and/ or HMB45 positivity. (Histologic differentiation of desmoplastic melanoma from cicatrices. Am J Dermatopathol. 1998;20(2):128-34)
The sclerotic/desmoplastic and hypopigmented blue naevi are uniformly positive for Melan-A, while desmoplastic melanoma is negative in the spindle cell compartment.
The nuclei in desmoplastic melanoma have a haphazard pattern and in scar tissue the nuclei have a parallel arrangement.
Spitzoid melanoma (cells are more plump) should also be excluded from spindle cell melanoma (cells are longer and thinner, less aggressive clinical behaviour).
Neurotropic melanoma is a rare variant of cutaneous melanoma.
The tumour has high incidence of local
recurrence and low rate of distant metastases
These tumour cells infiltrate around nerve bundles in the deep dermis and subcutaneous tissue. Hence the lesion is called neurotropic melanoma.
Often a combined desmoplastic and neurotropic patterns are present.
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