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Histology of Ewing’s Sarcoma

- Discussion:
    - small, round, neoplastic cells w/ large oval hyperchromatic nuclei;
    - vague indistinct (scant) cytoplasm & cytoplasmic membrane;
    - cells are usually spread out in thick sheets;
    - mitoses are common, and pseudorosette patterns are typical.
    - high cellularity, little intracellular stroma;
    - special stains:
          - PAS positive (due to staining of glycogen granules in the cytoplasm);
          - reticulum stain negative;
          - stains for S-100 protein
          - stains against neuron-specific enolase expression;
          - MIC-2 is a highly sensitive and specific marker for this family of tumors;
          - cytokeratin is an epithelial marker (should be negative)
          - vimentin is a mesenchymal marker (positive);
    - diff dx:
          - reticulum cell sarcoma;
          - neuroblastoma;
          - non-Hodgkin's lymphoma;
          - rhabdomyosarcoma