Immunohistochemical mismatch in a case of rhabdomyoblastic metastatic melanoma.

Melanomas can exhibit a wide range of unusual morphologies due to the neural crest origin of melanocytes. Several authors have documented variations in size and shape of cells, cytoplasmic features and inclusions, nuclear features and cell architecture. Metastatic melanoma with rhabdomyoblastic differentiation is an extremely rare condition with poor prognosis. Few studies concerning rhabdoid or rhabdomyoblastic differentiation in melanoma are currently available and the current report highlights some of the most important immunohistochemical features of this rare entity. We report on a case of a rhabdomyoblastic metastatic melanoma showing intense positivity for both melanocytic and rhabdoid markers in two cell populations dissociated within the tumor with multiple mismatches in immunomarker expression. Improved recognition of this rare morphological pattern may provide the means for developing new techniques to identify novel therapeutic targets, which would improve the prognostic outlook for these patients.