Spindle cells in herringbone pattern
Eosinophilic cytoplasm
Ovoid nuclei with mild pleomorphism; occasional mitotic activity
IHC: desmin, myogenin
RNA-seq: MEIS1::NCOA2 gene fusionÂ
Spindle cells in herringbone pattern
Eosinophilic cytoplasm
Ovoid nuclei with mild pleomorphism; occasional mitotic activity
Interspersed rhabdomyoblasts
IHC: desmin, myogenin
DNA-seq: MYOD1 mutation (c.365 T>G; p.Leu122Arg)Â
Spindle cells in herringbone pattern
Eosinophilic cytoplasm
Ovoid nuclei with mild pleomorphism; occasional mitotic activity
IHC: desmin, myogenin
DNA-seq: MYOD1 mutation (c.365 T>G; p.Leu122Arg)Â
Spindle cells in storiform-fascicular pattern
Pale eosinophilic cytoplasm
Ovoid nuclei with vesicular chromatin, and mild pleomorphism; inconspicuous mitotic activity
IHC: desmin, myogenin
RNA-seq: CITED2-rearrangementÂ
Spindle-epithelioid cells in fascicles
Abundant eosinophilic cytoplasmÂ
Round-ovoid nuclei with prominent nucleoli and moderate pleomorphism; conspicuous mitotic activity
IHC: desmin, myogenin, keratin (AE1/AE3), p63, ALK
RNA-seq: FUS::TFCP2 gene fusion
PMID: 29431183, 36374445
Spindle-epithelioid cells in fascicles
Abundant eosinophilic cytoplasmÂ
Round-ovoid nuclei with prominent nucleoli and moderate pleomorphism; conspicuous mitotic activity
IHC: desmin, myogenin, keratin (AE1/AE3)Â
RNA-seq: FUS::TFCP2 gene fusion
PMID: 29431183, 36374445
Spindle cell fascicles with variable cellularity
Abundant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
Collagenous stroma
RNA-seq: ZFP64::NCOA3 gene fusion
Spindle cell fascicles with variable cellularity
Abundant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
Collagenous stroma
IHC: desmin, SMA, CD34, S100
RNA-seq: ZFP64::NCOA3 gene fusion
PMID: 35521817
Spindle cell fascicles with variable cellularity
Abundant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; conspicuous mitotic activity
Areas of myxoid stroma, particularly around vessels
IHC: desminÂ
RNA-seq: ZFP64::NCOA3 gene fusion
PMID: 35521817
Spindle cell fascicles with variable cellularity
Abundant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
IHC: desmin, MyoD1; (myogenin negative)
RNA-seq: ZFP64::NCOA3 gene fusion
PMID: 35521817
Hypocellular spindle cell fascicles
Abundant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
Areas of hyalinization, particularly around vessels
IHC: desmin, MyoD1; (myogenin negative)
RNA-seq: ZFP64::NCOA3 gene fusion
PMID: 35521817
Short spindle cell fascicles; infiltrating native skeletal muscle
Scant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
IHC: desmin, myogenin
RNA-seq: PPARGC1A::VGLL3 gene fusion
PMID: 35766997
Short spindle cell fascicles; infiltrating native skeletal muscle
Scant eosinophilic cytoplasm with bipolar processes
Ovoid monomorphic nuclei; inconspicuous mitotic activity
IHC: desmin, myogenin
RNA-seq: EP300::VGLL3 gene fusion
PMID: 35766997
Infiltrative
Polygonal-spindle cells with vague fascicular-storiform pattern
Eosinophilic cytoplasm
Ovoid nuclei with occasional multinucleation and moderate pleomorphism; mitotic activity
IHC: desmin, myogenin
RNA-seq: EP300::VGLL3 gene fusion
PMID: 35766997
Spindle cell fascicles
Eosinophilic cytoplasmÂ
Ovoid-elongated nuclei with prominent nucleoli and mild pleomorphism; occasional mitotic activity
Interspersed rhabdomyoblasts with abundant dense eosinophilic cytoplasm and multiple nuclei; occasional thin-walled and ectatic vessels
IHC: desmin, myogenin
Spindle cell fascicles
Pale amphophilic cytoplasm
Hyperchromatic ovoid-elongated nuclei with prominent nucleoli and mild pleomorphism; occasional mitotic activity
Interspersed collagenous stroma
IHC: desmin, myogenin
Spindle cell fascicles
Pale amphophilic cytoplasm with indistinct cell borders
Hyperchromatic ovoid-elongated nuclei with mild pleomorphism; occasional mitotic activity
Interspersed rhabdomyoblasts with abundant dense eosinophilic cytoplasm; multiple peripheral nuclei; myxoid-collagenous stroma; ectatic thin-walled vasculature
IHC: desmin, myogenin