Pathology: solitary fibrous tumour

Solitary fibrous tumour

• Circumscribed; variably cellular; spindle cells in vague fascicles

• Scant pale eosinophilic cytoplasm

• Monomorphic elongated ovoid nuclei; inconspicuous mitotic activity 

• Collagenous-myxoid stroma with scattered 'starburst'-like fibers; ectatic and branching vessels, some with hyalinized walls

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed and lobulated; variably cellular; spindle cells with microcystic and fascicular patterns

• Scant pale eosinophilic cytoplasm

• Monomorphic elongated ovoid nuclei; mitotic activity 

• Collagenous-myxoid stroma with microcystic areas; rare ectatic and branching vessels

• IHC: STAT6, CD34

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed; regions of hyper- and hypo-cellularity; spindle cells with patternless architecture 

• Scant pale eosinophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Interspersed thick collagen bands; ectatic and branching vessels, some with hyalinized walls

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed; regions of hyper- and hypo-cellularity; spindle cells with patternless architecture 

• Scant pale eosinophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Interspersed thick collagen bands; ectatic and branching vessels, some with hyalinized walls

• IHC: CD34, STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed; regions of hyper- and hypo-cellularity; spindle cells with patternless architecture 

• Scant pale eosinophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Interspersed thick collagen bands; ectatic and branching vessels, some with hyalinized walls

• IHC: CD34

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed; cellular; spindle cells with fascicular-storiform pattern

• Scant pale eosinophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Inconspicuous vasculature; thin wispy collagen fibres

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, metastatic

• Circumscribed; cellular; spindle cells with patternless architecture 

• Eosinophilic cytoplasm

• Ovoid-elongated nuclei with scattered pleomorphism and multinucleation; occasional mitotic activity 

• Occasional thin branching vessels

• IHC: STAT6, CD34

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour

• Circumscribed; cellular; spindle cells with patternless architecture 

• Eosinophilic cytoplasm with vacuolation

• Monomorphic ovoid nuclei; inconspicuous mitotic activity 

• Occasional thin branching vessels with hyalinized walls

• IHC: CD34, STAT6

• RNA-seq: LRP1::STAT6 gene fusion*

* To date unreported in literature

Solitary fibrous tumour, cellular

• Cellular; epithelioid cells with patternless architecture 

• Scant eosinophilic cytoplasm

• Monomorphic ovoid nuclei with prominent nucleoli; occasional mitotic activity 

• Small ectatic thin-walled vessels

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, cellular

• Cellular; spindle cells with storiform pattern

• Scant pale amphophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Small ectatic thin-walled vessels

• IHC: CD34, STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, hypocellular

• Circumscribed; hypocellular; spindle cells in vague fascicles 

• Scant pale eosinophilic cytoplasm

• Monomorphic elongated ovoid nuclei; inconspicuous mitotic activity 

• Abundant thick bundles of collagen comprised of numerous delicate collagen fibres

• Small ectatic thin-walled vessels

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, lipomatous

• Circumscribed; hypocellular; spindle cells in vague fascicles 

• Scant pale eosinophilic cytoplasm

• Monomorphic elongated ovoid nuclei; inconspicuous mitotic activity 

• Abundant thick bundles of collagen comprised of numerous delicate collagen fibres

• Interspersed mature adipocytes

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, lipomatous

• Cellular; spindle cells with patternless distribution

• Scant eosinophilic cytoplasm

• Monomorphic ovoid nuclei with pin-point nucleoli; inconspicuous mitotic activity 

• Interspersed adipocytes, including some with vacuolated cytoplasm

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, myxoid

• Hypocellular; spindle-stellate cells with patternless distribution

• Abundant eosinophilic cytoplasm

• Ovoid nuclei with mild atypia and pin-point nucleoli; inconspicuous mitotic activity 

• Prominent myxoid stroma; extracellular myxoid pools

• IHC: STAT6

• RNA-seq: NAB2::STAT6 gene fusion

Solitary fibrous tumour, dedifferentiated

• Cellular; epithelioid cells with peritheliomatous pattern

• Scant eosinophilic cytoplasm with inconspicuous cell borders

• Ovoid nuclei with mild pleomorphism; conspicuous mitotic activity 

• Extensive necrosis

• IHC: STAT6, keratin (AE1/AE3)

• RNA-seq: NAB2::STAT6 gene fusion