Pathology: extraskeletal myxoid chondrosarcoma

Nests, chains and isolated round-rhabdoid cells

Eosinophilic cytoplasm

Eccentric reniform hyperchromatic nuclei with mild pleomorphism; mitotic activity

Abundant myxoid stroma

RNA-seq: EWSR1::NR4A3 gene fusion

Sheets, nests, and cords of round-rhabdoid cells

Eosinophilic cytoplasm

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

Abundant myxoid stroma

IHC: S100

RNA-seq: FUS::NR4A3 gene fusion

Sheets of round-epithelioid cells, with peritheliomatous pattern; loose fascicles of spindle cells

Eosinophilic cytoplasm

Round-ovoid nuclei with macronucleoli and mild pleomorphism; mitotic activity

Abundant necrosis

RNA-seq: TAF15::NR4A3 gene fusion

Anastomosing cords of epithelioid-stellate cells

Pale amphophilic cytoplasm with delicate processes

Small ovoid hyperchromatic nuclei with mild pleomorphism; inconspicuous mitotic activity

Abundant myxoid stroma

RNA-seq: EWSR1::NR4A3 gene fusion

Sheets of round-epithelioid cells

Dense eosinophilic and granular cytoplasm

Round-ovoid nuclei with macronucleoli and mild pleomorphism; mitotic activity

RNA-seq: EWSR1::NR4A3 gene fusion

Sheets of round-epithelioid cells

PAmphophilic cytoplasm with indistinct cell borders

Round-ovoid nuclei with prominent nucleoli and mild pleomorphism; rare mitotic activity

Delicate thin-walled vasculature

RNA-seq: EWSR1::NR4A3 gene fusion

Nests and broad anastomosing cords of epithelioid-stellate cells

Pale amphophilic cytoplasm

Round-ovoid nuclei with prominent nucleoli and mild pleomorphism; inconspicuous mitotic activity

Abundant myxoid stroma

RNA-seq: EWSR1::NR4A3 gene fusion

Anastomosing cords of epithelioid-spindle cells

Pale amphophilic cytoplasm with delicate processes

Small ovoid hyperchromatic nuclei with mild pleomorphism; inconspicuous mitotic activity

Abundant myxoid stroma

RNA-seq: EWSR1::NR4A3 gene fusion