ERBB4 and malignant peripheral nerve sheath tumor: Recent evidence suggests involvement of RTKs such as PDGFR [29, 36, 37], c-Met [38], Axl [39], IGF1-R [40], EphB4 [41] and ErbB4 [42] as driver kinases in different sarcoma subtypes including synovial sarcoma, Ewing sarcoma as well as malignant peripheral nerve sheath tumor (MPNST).