This man developed a slowly growing ill-defined mass on his shoulder. Clear cell sarcoma (or melanoma of soft parts) is extremely rare. They are dermal or deep-seated tumors. Its histogenesis is somewhat unclear, but probably originates from the neural crest. There are many overlapping features with melanoma (including s-100, SOX-10 positivity and melanosomes by electron microscopy). There is a characteristic chromosomal translocation, t(12;22), which results in EWSR1/ATF chimeric gene. The histologic differential diagnosis includes metastatic melanoma or a malignant peripheral nerve sheath tumor, due to strong s-100 positivity. Use of electron microscopy and FISH analysis can help with difficult cases. The clinical course is like most sarcomas, where local control is key, but difficult. Recurrences and metastases are common.
This magnification highlights the clear-cell spindled morphology, typical of this tumor. The nuclei have open chromatin and prominent nucleoli.