PMC8387072_01
Histopathology and Immunohistochemistry. A - Low power photomicrograph of a hematoxylin and eosin stain shows the nodular architecture of the tumor with hypercellular and hypocellular regions with increased cellularity at the periphery of the lobules. The right side of the image shows pale blue myxoid matrix representing hypocellular areas. The left side, more eosinophilic appearing, shows both organoid and lobular growth patterns (2x objective); B - Abundant myxoid stroma with uniform cells arranged in trabeculae and interconnecting cords (20x objective); C - Rhabdoid cells with eccentrically located nuclei and eosinophilic to finely vacuolated cytoplasm (40x objective); D - CD34 immunohistochemical stain depicts tumor cells with intense cell membrane staining (20x objective).
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Tumor was noted to focally infiltrate the surrounding fibrofatty tissue and was present at the inked surgical resection surface (Figures 1A-1C).
Fluorescence in Situ Hybridization (FISH). A - FISH analysis showing EWSR1 gene rearrangement at the 22q12 locus. The 5' segment of the probe is orange and the 3' segment green. In the inset, a magnified cell nucleus from the field shows a split probe on one chromosome (two distinctly separate orange and green dots) and an intact probe (arrow) on the other (fused orange and green signals); B - FISH analysis depicting NR4A3 (9q22.33-q31.1) gene rearrangement using another break-apart probe. The 5' segment of the probe is orange and the 3' segment is green. The arrows in the insets (1 & 2) point to the intact gene on one chromosome and a broken apart gene on the other chromosome.
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EWSR1 FISH was performed and was positive for EWSR1 rearrangement, consistent with a diagnosis of extraskeletal myxoid chondrosarcoma (Figure 2A). Positive NR4A3 gene rearrangement by FISH was further supportive of extraskeletal myxoid chondrosarcoma (Figure 2B).