Pathology: Ewing sarcoma

Ewing sarcoma

  • Sheets-nests of small round cells

  • Scant eosinophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and mild pleomorphism; mitotic activity

  • Occasional thin fibrovascular septa

  • IHC: S100, CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Sheets-nests of small round-polygonal cells

  • Scant eosinophilic cytoplasm

  • Round-ovoid nuclei with vescicular chromatin, small nucleoli and mild pleomorphism; mitotic activity

  • Delicate thin-walled vasculature

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Sheets of small round cells with occasional rosettes and pseudorosettes

  • Scant eosinophilic cytoplasm

  • Round-ovoid nuclei with vescicular chromatin, small nucleoli and mild pleomorphism; mitotic activity

  • Small thin-walled vasculature; necrosis

  • IHC: CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Sheets-nests of small round cells

  • Scant amphophilic cytoplasm

  • Monomorphic round-ovoid nuclei with small nucleoli; mitotic activity

  • Delicate branching vasculature

  • IHC: CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

  • PMID: 21649689

Ewing sarcoma

  • Sheets and nests of epithelioid cells

  • Scant amphophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and moderate pleomorphism; mitotic activity

  • Areas of desmoplastic fibrous stroma

  • IHC: CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Sheets of small round cells with pseudorosettes and subtle rosettes

  • Scant eosinophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and mild pleomorphism; mitotic activity

  • Small thin-walled vasculature; necrosis

  • IHC: CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Sheets of epithelioid cells

  • Minimal amphophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and moderate pleomorphism; mitotic activity

  • Prominent thin-walled vessels with hyalinization

  • IHC: CD99

  • RNA-seq: EWSR1::FLI1 gene fusion

Ewing sarcoma

  • Small round cells in sheets-nests with occasional pseudoacini

  • Scant amphophilic cytoplasm

  • Round nuclei with small nucleoli and mild pleomorphism; inconspicuous mitotic activity

  • Delicate fibrovascular septa

  • IHC: ERG

  • RNA-seq: FUS::ERG gene fusion

  • PMID: 34747554

Ewing sarcoma

  • Nests of epithelioid cells

  • Scant amphophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and moderate pleomorphism; mitotic activity

  • Prominent hyaline stroma; ectatic thin-walled vasculature

  • IHC: CD99, ERG

  • RNA-seq: EWSR1::ERG gene fusion

Ewing sarcoma

  • Sheets and anastomosing cords of epithelioid cells

  • Scant amphophilic cytoplasm

  • Round-ovoid nuclei with small nucleoli and moderate pleomorphism; mitotic activity

  • Prominent hyaline stroma; ectatic thin-walled vasculature

  • RNA-seq: EWSR1::ERG gene fusion

Ewing sarcoma

  • Sheets-nests of small round-rhabdoid cells

  • Scant eosinophilic cytoplasm

  • Eccentric round-reniform nuclei with mild pleomorphism; mitotic activity

  • Delicate branching vasculature

  • IHC: synaptophysin, CD99

  • RNA-seq: EWSR1::FEV gene fusion