Microscopic Description -- Skeletal/Soft Tissue Pathology Case


Sections of tumor showed interweaving fascicles of spindle cells (Figures07 and 09) having prominent eosinophilic, fibrillary cytoplasm, cigar-shaped nuclei, and having blunt endings (Figure 08). There was only mild atypia in the spindle cells. No necrosis was identified. A nonspecific storiform pattern was also present, and the background stroma is variably collagenized (Figures 07 and 09). Occasionally, the neoplastic cells are more rounded, with pale to clear cytoplasm showing epithelioid features (Figure 10). Mitotic figures were 1-2 per 10 high-power fields. The peripheral border of the neoplasm showed osteoclast-like giant cells either interspersed in the neoplastic stroma or adjacent to areas of cancellous and cortical bone destruction (Figures 11 and 12). Focal breaching of the cortical bone was identified (Figure 13), however, the inked resection margins were free from tumor involvement.


The tumor cells were immunoreative for both common muscle actin (HHF-35) (Figures 14 and 15) and desmin (Figure 16). The CD34 immunostain decorated thin-walled vessels inside the tumor, but the tumor cells showing no immunoreactivity (Figure 17). Reticulin stain showed distinct interstitial reticulin fibers wrapped around each individual neoplastic cells (Figure 18). Immunostains for cytokeratin (AE1/AE3) and S100 protein were negative. Ki67 immunostain, a proliferation marker, showed increased nuclear staining in leiomyosarcoma (Figure 20) as compared to rare nuclear staining in leiomyoma (Figure 19).



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