Pathology: angiomatoid fibrous histiocytoma

Circumscribed; fascicles of epithelioid-spindle cells

Pale amphophilic cytoplasm

Ovoid-elongated nuclei with small nucleoli and mild atypia; inconspicuous mitotic activity

Central cystic haemorrhagic cavity; abundant haemosiderin deposition; peripheral lymphocytic cuff

IHC: desmin

RNA-seq: EWSR1::CREB1 gene fusion

Epithelioid-spindle cells with storiform pattern

Pale amphophilic cytoplasm

Ovoid nuclei with small nucleoli and mild atypia; inconspicuous mitotic activity

Focal myxoid-collagenous stroma; interspersed lymphoplasmacytic infiltrate

IHC: desmin, epithelial membrane antigen

RNA-seq: EWSR1::CREB1 gene fusion

Circumscribed

Spindle cells with fascicular pattern

Pale eosinophilic cytoplasm

Ovoid nuclei with small nucleoli and minimal atypia; inconspicuous mitotic activity

Occasional broad collagen bands; incomplete lymphocytic cuff

SS: Prussian blue

IHC: smooth muscle actin, desmin, H-caldesmon, epithelial membrane antigen

RNA-seq: EWSR1::ATF1 gene fusion

Multinodular; fascicles of epithelioid-polygonal cells

Pale eosinophilic cytoplasm

Ovoid nuclei with small nucleoli, vesicular chromatin and mild atypia; inconspicuous mitotic activity

Central cystic cavity; abundant haemosiderin deposition; siderophages and foamy histiocytes; peripheral lymphocytic cuff

FISH: EWSR1-rearrangement

Circumscribed; ovoid cells in short fascicles and whorls

Pale amphophilic cytoplasm

Ovoid nuclei with small nucleoli, vesicular chromatin and mild atypia; inconspicuous mitotic activity

Central cystic cavity; abundant haemosiderin deposition; siderophages and foamy histiocytes; peripheral lymphocytic cuff

IHC: desmin

RNA-seq: EWSR1::CREB1 gene fusion

Ovoid-spindle cells with vague storiform pattern

Pale amphophilic cytoplasm

Ovoid nuclei with small nucleoli, vesicular chromatin and mild atypia; inconspicuous mitotic activity

Peripheral hint of haemorrhagic cavity; interspersed lymphocytes and histiocytes

RNA-seq: EWSR1::CREB1 gene fusion