Because novel therapeutic options are limited in Ewing sarcomas (ES), we investigated the expression, genetic aberrations and clinical relevance of MET and anaplastic lymphoma kinase (ALK) in ES and determined the relevance of targeting these receptors. MET and ALK protein expression was determined immunohistochemically in 31 (50 samples) and 36 (59 samples) ES patients, respectively. Samples included primary tumors, postchemotherapy resections, metastases and relapses. MET and ALK RTK domains were sequenced in respectively 33 and 32 tumors. Five ES cell lines were treated in vitro with the MET/ALKinhibitor crizotinib, the ALK-inhibitor NVP-TAE684 or the MET-inhibitor cabozantinib and analyzed by MTT assays. Modest to high MET and ALK expression was detected in the majority of ES (86 and 69%, respectively). ALK expression was significantly lower in postchemotherapy resections compared to paired untreated primary tumors (p 5 0.031, z 5 22.310, n 5 11). In primary tumors (n 5 20), membranous MET expression significantly correlated with a poor overall survival (OS) (60 vs. 197 months, p 5 0.014). There was a trend toward a poor event-free survival (67 vs. 111 months, p 5 0.078) and OS (88 vs. 128 months, p 5 0.074) in patients with highest ALK levels (n 5 29). ALK or MET RTK domain aberrations were demonstrated in 5/32 (16%) and 3/33 (9%) tumors, respectively. Crizotinib (IC 50 1.22-3.59 lmol/L), NVP-TAE684 (IC 50 0.15-0.79 lmol/L) and cabozantinib (IC 50 2.69-8.27 lmol/L) affected ES cell viability in vitro. Altogether, our data suggest that MET and ALK are potential novel therapeutic targets in ES and targeting these receptors may be of great interest to rationally design future studies in ES.Ewing sarcoma (ES) is the second most common primary malignant bone tumor occurring in children and adolescents. Although multimodal treatment has improved the prognosis of patients with localized ES during the last decades, the final outcome has not improved for patients with metastatic disease and side effects of treatment could be severe. 1,2 This urges the need for novel therapeutic strategies, including targeted therapies directed against molecules involved in the pathogenesis and progression of ES, 3 Although at present some receptor tyrosine kinases (RTKs) have been implicated in ES, predominantly the insulin-like growth factor-1 receptor (IGF-1R), and to a lesser extent also platelet-derived growth factor receptor (PDGFR) and c-KIT, the role of several other receptors remains to be investigated. 4 In this study, we addressed the role of MET and anaplastic lymphoma kinase (ALK) in ES.MET is a RTK known to be deregulated in many cancers. At present, the hepatocyte growth factor (HGF) is the only known ligand for MET. Upon receptor binding, MET undergoes rapid tyrosine phosphorylation and several intracellular signaling cascades are activated, including the phosphatidylinositol 3 (PI3)/Akt kinase and extracellular signal regulated kinase (Erk) pathways. Several studies have shown that HGF/ MET signaling is involved in c...