The diagnosis of metastatic melanoma may be challenging, particularly in tumors where all melanocytic markers are negative. In addition, de-differentiated, trans-differentiated, and undifferentiated melanomas may show divergent differentiation and aberrant immunoreactivity. PRAME is an antigen that has been described in primary cutaneous and metastatic melanomas and has become a useful ancillary immunohistochemical marker, particularly when all others are negative. We present a patient with metastatic melanoma to the left atrium with loss of melanocytic differentiation, gain of a rhabdomyosarcomatous differentiation, and a diffuse and strong positivity for PRAME.
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