Pathology: intra-osseous rhabdomyosarcoma

Intra-osseus rhabdomyosarcoma

• Fascicles of spindle-epithelioid cells

• Eosinophilic cytoplasm

• Round-ovoid nuclei with minimal pleomorphism; inconspicuous mitotic activity

• Occasional large epithelioid cells with abundant eosinophilic cytoplasm; delicate thin-walled vasculature

• IHC: desmin, myogenin

• RNA-seq: MEIS1-NCOA2 gene fusion

• PMID: 30720533

Intra-osseus rhabdomyosarcoma

• Short fascicles of spindle-epithelioid cells

• Amphophilic cytoplasm

• Eccentric round-ovoid nuclei with mild pleomorphism; mitotic activity

• IHC: desmin, myogenin, ALK

• RNA-seq: FUS-TFCP2 gene fusion

• PMID: 32556562

ALK overexperession may be exploited therapeutically (PMID: 31965718)