Pathology: undifferentiated / unclassified sarcomas

Undifferentiated spindle cell sarcoma

  • Spindle cells with herringbone pattern

  • Eosinophilic cytoplasm

  • Ovoid hyperchromatic nuclei with prominent nucleoli and moderate pleomorphism; brisk mitotic activity

  • Necrosis

Undifferentiated round cell sarcoma

  • Sheets of small round cells

  • Pale eosinophilic cytoplasm with indistinct cell borders

  • Monomorphic round nuclei with speckled chromatin and small nucleoli; mitotic activity

  • Cystic degeneration with pools of proteinaceous fluid

  • RNA-seq: negative

Undifferentiated epithelioid cell sarcoma

  • Sheets and nests of epithelioid cells

  • Amphophilic cytoplasm

  • Round-ovoid nuclei with moderate pleomorphism; mitotic activity

  • Prominent clefting; necrosis

  • RNA-seq: negative

Undifferentiated pleomorphic cell sarcoma

  • Sheets of polygonal-spindle cells with a vague storiform-fascicular pattern

  • Abundant eosinophilic cytoplasm

  • Round-ovoid hyperchromatic nuclei with frequent multinucleation and marked pleomorphism; brisk mitotic activity

  • Necrosis; mild chronic inflammation