clear cell sarcoma

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  • Clinical

    • age: young adults, peak 30-40s
    • site: extremities (90%), esp foot/ankle, usually attached to tendons, aponeuroses
    • melanocytic differentiation, unrelated to clear cell sarcoma of kidney
  • Histology

    • architecture: nests with fibrous septa, fascicles
    • cytology: polygonal, spindled, pink or clear cytoplasm, vesicular nuclei, prominent nucleoli
    • rare variants: spindle cell, pleomorphic, solid round cell, microcystic, myxoid stroma
  • Stains

    • positive: S100, HMB45
  • Ddx

    • melanoma lacks EWSR1
  • Molecular

    • t(12;22)(q13;q12), EWSR1/ATF1 fusion
    • EWS 22q12
    • ATF1 12q13
    • gastrointestinal variant: EWSR1/CREB1