NTRK3 and congenital fibrosarcoma: Among the fusion genes frequently identified in soft tissue tumors are SS18 (synovial sarcoma 18)-SSX (synovial sarcoma X) in synovial sarcoma, EWSR1 (EWS RNA binding protein 1)-FLI1 (friend leukemia virus integration 1) in Ewing sarcoma, PAX (paired box)-FOXO1 (forkhead box O1) in rhabdomyosarcoma, and ETV6-NTRK3 (neurotrophic receptor tyrosine kinase 3) in congenital fibrosarcoma.