Sheets of spindle-round cells
Scant amphophilic cytoplasm
Ovoid-round nuclei with small nucleoli and moderate pleomorphism; mitotic activity
Ectatic vessels with perivascular hyalinization
IHC: CD99
RNA-seq: EWSR1::FLI1 gene fusion
Sheets and cords of round cells
Scant amphophilic cytoplasm
Round-ovoid hyperchromatic nuclei with moderate pleomorphism; occasional mitotic activity
Collagenous stroma, with ostoid matrix
IHC: CD99, desmin, p63
RNA-seq: EWSR1::FLI1 gene fusion
Sheets of small round cells
Scant eosinophilic cytoplasm
Round-ovoid nuclei with small nucleoli and mild pleomorphism; mitotic activitiyÂ
IHC: CD99
RNA-seq: EWSR1::FLI1 gene fusion
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
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
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
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
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
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
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
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
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
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
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