Clear cell sarcoma shows immunoreactivity for microphthalmia transcriptionfactor: Further evidence for melanocytic differentiation

Microphthalmia transcription factor, a melanocytic nuclear protein critical for the embryonic development and postnatal viability of melanocytes, is a master regulator in modulating extracellular signals. Recently, microphtha lmia transcription factor expression was shown to be both a sensitive and s pecific marker of epithelioid melanoma. We investigated the sensitivity of D5, an anti-microphthalmia transcription factor antibody, for diagnosis of clear cell sarcoma (also known as malignant melanoma of soft parts). Immuno reactivity in a nuclear pattern for D5 was present in 8 of 12 (75%) tumors. D5 staining was strong fn three tumors, moderate in two, and weak in three . S-100 protein expression was seen in all 12 cases that had clear cell sar coma examined. HMB-45 staining was seen in 11 of 12 (92%) tumors. Focal Mel an-A positivity was seen in 3 of 7 (43%) tumors. Although D5 was shown in a previous study to be a highly sensitive and specific marker for epithelioi d melanomas, the results of this study expand the spectrum of tumors showin g immunoreactivity for D5. D5 immunoreactivity in clear cell sarcoma provid es further evidence for melanocytic differentiation in this unusual tumor.