Neurotropic Melanoma. A variant of desmoplastic melanoma

In ten cases of neurotropic melanoma, patients presented with nodules composed of amelanotic, deeply infiltrating neuroid fascicles. Only four cases were clinically suggestive of melanoma. In eight of the tumors, a precursor lesion was found histologically and provided a major clue to the diagnosis. In seven cases, the dysplastic precursor was lentiginous, while a superficial spreading pattern was present in one. Initial surgery was often inadequate because of the difficulty in defining tumor margins and the lack of pigment. In seven of the tumors, S100 protein was demonstrated within the invasive spindle cell component by the immunoperoxidase method. This finding was negative in three cases, two of which showed positive staining of the precursor and nerve filaments, indicating that the absence of S100 protein cannot be used as an exclusion criterion for neurotropic melanoma.