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Endoglin (ENG) is a mesenchymal stem cell (MSC) marker typically expressed by active endothelium. This transmembrane glycoprotein is shed by matrix metalloproteinase 14 (MMP14). Our previous work demonstrated potent preclinical activity of first-in-class anti-ENG antibody-drug conjugates as a nascent strategy to eradicate Ewing sarcoma (ES), a devastating rare bone/soft tissue cancer with a putative MSC origin. We also defined a correlation between ENG and MMP14 expression in ES. Herein, we show that ENG expression is significantly associated with a dismal prognosis in a large cohort of ES patients. Moreover, both ENG/MMP14 are frequently expressed in primary ES tumors and metastasis. To deepen in their functional relevance in ES, we conducted transcriptomic and proteomic profiling of in vitro ES models that unveiled a key role of ENG and MMP14 in cell mechano-transduction. Migration and adhesion assays confirmed that loss of ENG disrupts actin filament assembly and filopodia formation, with a concomitant effect on cell spreading. Furthermore, we observed that ENG regulates cell-matrix interaction through activation of focal adhesion signaling and protein kinase C expression. In turn, loss of MMP14 contributed to a more adhesive phenotype of ES cells by modulating the transcriptional extracellular matrix dynamics. Overall, these results suggest that ENG and MMP14 exert a significant role in mediating correct spreading machinery of ES cells, impacting the aggressiveness of the disease., E.A.’s laboratory is supported by ISCIII-FEDER (PI20/00003), CIBERONC (CB16/12/00361), PAIDI-Junta de Andalucía (P18-RT-735), Fundación CRIS Contra el Cáncer, Asociación Candela Riera and Asociación Pablo Ugarte. A.T.A. is supported by Juan de la Cierva Incorporación fellowship (IJC-2018-036767-I); P.P.-C. is sponsored by the Fundación María García Estrada. J.O.-P is supported by Ph.D. Grant Plan Propio from the University of Seville. J.D.-M is supported by CIBERONC (CB16/12/00361). C.S.-A. is supported by the European Social Fund and the Junta de Andalucía (Talento Doctores 2020, DOC_01473). This work was supported by grants from the Consejería de Salud (Junta de Andalucía, grants No PI-0036-2017, PI-0040-2017, and PI-0061-2020) awarded to J.D.-M, A.T.A. and C. S.-A., respectively. This work was also supported by the GEIS-Fundación Mari Paz Jiménez Casado (IV beca trienal) granted to J.D.-M, the 13ª GEIS-Beca Buesa granted to A.T.A. and CRIS (Cancer Research Innovation Spain) granted to J.D.-M and E.A. The laboratory of T.G.P.G. is supported by the Barbara and Wilfried Mohr Foundation. The lab of J.A. is supported by the Instituto de Salud Carlos III (ISCIII), grant number PI20CIII/00020; Asociación Pablo Ugarte, grant numbers TRPV205/18, TPI-M 1149/13; Asociación Candela Riera; Asociación Todos Somos Iván & Fundación Sonrisa de Alex, grant reference: TVP333-19.

© 2020 by the authors., Ewing sarcoma is a highly aggressive round cell mesenchymal neoplasm, most often occurring in children and young adults. At the molecular level, it is characterized by the presence of recurrent chromosomal translocations. In the last years, next-generation technologies have contributed to a more accurate diagnosis and a refined classification. Moreover, the application of these novel technologies has highlighted the relevance of intertumoral and intratumoral molecular heterogeneity and secondary genetic alterations. Furthermore, they have shown evidence that genomic features can change as the tumor disseminates and are influenced by treatment as well. Similarly, next-generation technologies applied to liquid biopsies will significantly impact patient management by allowing the early detection of relapse and monitoring response to treatment. Finally, the use of these novel technologies has provided data of great value in order to discover new druggable pathways. Thus, this review provides concise updates on the latest progress of these breakthrough technologies, underscoring their importance in the generation of key knowledge, prognosis, and potential treatment of Ewing Sarcoma., This work was supported by grants from the Consejería de Salud (Junta de Andalucía, grants No PI-0036-2017 and PI-0040-2017) awarded to JDM and ATA, respectively; by grants from the Asociación Pablo Ugarte, Fundación María García Estrada and FARO niños con cáncer to JDM and EdA. EdA’s laboratory is supported by the AECC project (GCB13-1578), ISCIIIFEDER (PI14/01466, PI17/00464), CIBERONC (CB16/12/00361) and Fundación CRIS Contra el Cáncer. This work was also supported by a Juan de la Cierva Incorporación fellowship (IJC-2018-036767-I) to ATA, and a pre-doctoral fellowship from the VI Plan Propio from the Universidad de Sevilla to JOP.

YAP1 and TAZ (WWTR1) oncoproteins are the final transducers of the Hippo tumor suppressor pathway. Deregulation of the pathway leads to YAP1/TAZ activation fostering tumorigenesis in multiple malignant tumor types, including sarcoma. However, oncogenic mutations within the core components of the Hippo pathway are uncommon. Ewing sarcoma (EwS), a pediatric cancer with low mutation rate, is characterized by a canonical fusion involving the gene EWSR1 and FLI1 as the most common partner. The fusion protein is a potent driver of oncogenesis, but secondary alterations are scarce, and little is known about other biological factors that determine the risk of relapse or progression. We have observed YAP1/TAZ expression and transcriptional activity in EwS cell lines. Analyses of 55 primary human EwS samples revealed that high YAP1/TAZ expression was associated with progression of the disease and predicted poorer outcome. We did not observe recurrent SNV or copy number gains/losses in Hippo pathway-related loci. However, differential CpG methylation of the RASSF1 locus (a regulator of the Hippo pathway) was observed in EwS cell lines compared with mesenchymal stem cells, the putative cell of origin of EwS. Hypermethylation of RASSF1 correlated with the transcriptional silencing of the tumor suppressor isoform RASFF1A, and transcriptional activation of the pro-tumorigenic isoform RASSF1C, which promotes YAP1/TAZ activation. Knockdown of YAP1/TAZ decreased proliferation and invasion abilities of EwS cells and revealed that YAP1/TAZ transcription activity is inversely correlated with the EWS–FLI1 transcriptional signature. This transcriptional antagonism could be explained partly by EWS–FLI1-mediated transcriptional repression of TAZ. Thus, YAP1/TAZ may override the transcriptional program induced by the fusion protein, contributing to the phenotypic plasticity determined by dynamic fluctuation of the fusion protein, a recently proposed model for disease dissemination in EwS. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland., This work was sup-ported by a grant from the Fundación Pública Andaluza Progreso y Salud (Junta de Andalucía) and JANSSEN CILAG, S.A. (grant No PI-0344-2014) to JDM. PRN is a PhD student recipient of a PFIS fellowship to Enrique de Alava (grant No F109/00193).JDM, LRP, and ATM are PhD researchers funded bythe Asociación Española Contra el Cáncer (AECC,GCB13-1578). CJ works as a laboratory technician supported by the ISCIII. EDA’s laboratory is sup-ported by the AECC project (GCB13 -1578), ISCIII -FEDER (PI14/014 66, PI17/ 00464), C IBERONC(CB16/12/00361) , Asociación Pablo Ugarte, and Fundación María García Estrada. The laboratory of TGPGis supported by the ‘Verein zur Förderung von Wis-senschaft und Forschung an der Medizinischen Fakul-tät der LMU München’ (WiFoMed), by LMUMunich’s Institutional Strategy LMUexcellent withinthe framework of the German Excellence Initiative,the ‘Mehr LEBEN fü r krebs kranke Kin der – Bettina-Bräu-Stiftung’ to TGPG, the Kind-Philipp-Foundation, the Matthias-Lackas Foundation, the Dr Rolf MSchwiete Foundation, the Dr Leopold and CarmenEllinger Foundation, the Wilhelm-Sander-Foundation(2016.167.1), the German Cancer Aid (DKH-70112257), the Gert und Susanna Mayer Fou ndation,and the Deutsche Forschungsgemeinschaft (DFG-391665916) . JA’s laboratory is supported by Institutode Salud Carlos III (PI16CIII/00026, DTS18CIII/00005), Asociación Pablo Ugarte ( TPY-M 1149/13;TRPV 205/18 ), ASION (TVP 1 41/17), Fundación Sonrisa de Alex, and Todos somos Iván (TVP 1324/15). We thank Dr Stefano Piccolo for the lucif-erase reporter plasmid with TEAD motifs (Addgeneplasmid # 34615), Dr Mark Bond for providing theplasmid pTNT-min, and Dr Campana for the hMSCTERT cell line

The Hippo pathway is an evolutionarily conserved modulator of developmental biology with a key role in tissue and organ size regulation under homeostatic conditions. Like other signaling pathways with a significant role in embryonic development, the deregulation of Hippo signaling contributes to oncogenesis. Central to the Hippo pathway is a conserved cascade of adaptor proteins and inhibitory kinases that converge and regulate the activity of the oncoproteins YAP and TAZ, the final transducers of the pathway. Elevated levels and aberrant activation of YAP and TAZ have been described in many cancers. Though most of the studies describe their pervasive activation in epithelial neoplasms, there is increasing evidence pointing out its relevance in mesenchymal malignancies as well. Interestingly, somatic or germline mutations in genes of the Hippo pathway are scarce compared to other signaling pathways that are frequently disrupted in cancer. However, in the case of sarcomas, several examples of genetic alteration of Hippo members, including gene fusions, have been described during the last few years. Here, we review the current knowledge of Hippo pathway implication in sarcoma, describing mechanistic hints recently reported in specific histological entities and how these alterations represent an opportunity for targeted therapy in this heterogeneous group of neoplasm., E.d.Á.’s laboratory is supported by ISCIIIFEDER (PI20/00003) to E.d.Á., Consejería de Salud y Familias, Junta de Andalucía (PE-0186-2018) to E.d.Á. and (PI-0061-2020) to C.S.-A. and E.d.Á., GEIS (Beca José María Buesa) to A.T.A., GEIS-Fundación Mari Paz Jiménez Casado (Beca Trienal a la Investigación en Sarcomas) to J.D.-M., Fundación CRIS Contra el Cáncer, Asociación Pablo Ugarte, Fundación María García Estrada and CIBERONC. C.S.-A. is supported by the European Social Fund and the Junta de Andalucía (Talento Doctores 2020, DOC_01473), J.O.-P. is granted by a pre-doctoral fellowship from the VI Plan Propio from the Universidad de Sevilla; A.T.A. is supported Juan de la Cierva Incorporación fellowship (IJC-2018-036767-I), and J.D.-M. is supported by CIBERONC (CB16/12/00361).

This article belongs to the Special Issue Diagnosis and Treatment for Bone Tumor and Sarcoma., [Simple Summary] A solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that can arise at any body location. Local or distant recurrences occur in a significant proportion of cases, but these recurrences are difficult to predict using clinical or pathological features. A specific genetic alteration, the gene fusion NAB2-STAT6, is considered to be the defining driver mutation, and different fusion variants seem to account for specific clinical and pathological features, but their prognostic value remains controversial. We inspected a series of 83 SFTs with a high rate of recurrence to evaluate the clinical significance of several potential biomarkers in addition to gene fusion. Our findings confirm previous observations and uncover novel associations of molecular alterations with clinical features, adding additional evidence for their potential application as molecular biomarkers that are helpful to predict the course of the disease., [Abstract] Risk stratification of solitary fibrous tumor (SFT) patients based on clinicopathological features has limited efficacy, especially in predicting late relapse or metastasis. The hallmark alteration of SFT is the gene fusion NAB2-STAT6, whose prognostic value remains controversial. As biological knowledge of this entity has increased in recent years, new molecular alterations have emerged that could be helpful to refine current risk models. Here, we evaluated NAB2-STAT6 fusion variants and other molecular alterations in a series of 83 SFTs that are enriched in progressing cases. Gene fusion variants were identified by targeted RNA-seq in the whole series, whereas TERT promoter (pTERT) mutations were inspected by Sanger sequencing in a subset of 18 cases. Immunohistochemical assays were performed to assess BCOR and NTRK expression as well as P53 mutation status in 45, 44, and 44 cases, respectively. While confirming the associations of gene fusion variants with clinicopathological parameters, our results do not prove their prognostic value. Pan-TRK immunoexpresion correlated with recurrence/progression, P53 staining associated with higher mitotic counts, and pTERT mutations were enriched in cases with fatal outcome. An intriguing correlation was found for BCOR protein expression with gene fusion variants, size, and tumor location., This research was funded by the Junta de Andalucía (PI-0061-2020) to C.S.-A. and E.A. and the GEIS-Fundación Mari Paz Jiménez Casado (IV beca trienal) to J.D.-M., C.S.-A. was supported by the European Social Fund and the Junta de Andalucía (Talento Doctores 2020, DOC_01473), and J.D.-M. was supported by CIBERONC (CB16/12/00361). E.d.Á.’s laboratory is supported by the ISCIII-FEDER (PI20/00003), CIBERONC (CB16/12/00361), Asociación Pablo Ugarte, Fundación CRIS contra el cancer, Asociación Candela Riera, and Fundación María García Estrada.

Chemotherapy is one of the most established and effective treatments for almost all types of cancer. However, the elevated toxicity due to the non-tumor-associated effects, development of secondary malignancies, infertility, radiation-induced fibrosis and resistance to treatment limit the effectiveness and safety of treatment. In addition, these multiple factors significantly impact quality of life. Over the last decades, our increased understanding of cancer epigenetics has led to new therapeutic approaches and the promise of improved patient outcomes. Epigenetic alterations are commonly found in cancer, especially the increased expression and activity of histone deacetylases (HDACs). Dysregulation of HDACs are critical to the development and progression of the majority of tumors. Hence, HDACs inhibitors (HDACis) were developed and now represent a very promising treatment strategy. The use of HDACis as monotherapy has shown very positive pre-clinical results, but clinical trials have had only limited success. However, combinatorial regimens with other cancer drugs have shown synergistic effects both in pre-clinical and clinical studies. At the same time, these combinations have enhanced the efficacy, reduced the toxicity and tumor resistance to therapy. In this review, we will examine examples of HDACis used in combination with other cancer drugs and highlight the synergistic effects observed in recent preclinical and clinical studies., This work was supported by Instituto de Salud Carlos III_FEDER (PI17/00464 and CB16/12/00361), by the Consejería de Salud, Junta de Andalucía (PI-0013-2018), and by Fundación María García Estrada.

[Purpose] Epigenetic regulation is crucial in mammalian development and maintenance of tissue-cell specific functions. Perturbation of epigenetic balance may lead to alterations in gene expression, resulting in cellular transformation and malignancy. Previous studies in Ewing sarcoma (ES) have shown that the Nucleosome Remodeling Deacetylase (NuRD) complex binds directly to EWS-FLI1 oncoprotein and modulates its transcriptional activity. The role of EWS-FLI1 as a driver of proliferation and transformation in ES is widely known, but the effect of epigenetic drugs on fusion activity remains poorly described. The present study evaluated the combination effects of the histone deacetylases inhibitor suberoylanilide hydroxamic acid (SAHA) and Lysine-specific demethylase1 inhibitor (HCI-2509) on different biological functions in ES and in comparison to monotherapy treatments., [Results] The study of proliferation and cell viability showed a synergistic effect in most ES cell lines analyzed. An enhanced effect was also observed in the induction of apoptosis, together with accumulation of cells in G1 phase and a blockage of the migratory capacity of ES cell lines. Treatment, either in monotherapy or in combination, caused a significant decrease of EWS-FLI1 mRNA and protein levels and this effect is mediated in part by fusion gene promoter regulation. The anti-tumor effect of this combination was confirmed in patient-derived xenograft mouse models, in which only the combination treatment led to a statistically significant decrease in tumor volume., [Conclusions] The combination of SAHA and HCI-2509 is proposed as a novel treatment strategy for ES patients to inhibit the essential driver of this sarcoma and tumor growth., Research in EDA, JM, and OMT labs is supported by Asociación Española Contra el Cáncer (AECC). Enrique de Alava’s lab is also supported by the Ministry of Economy and Competitiveness of Spain-FEDER (CIBERONC, PI11700464, RD06/0020/0059, FMGE) and the European Commission (FP7-HEALTH-2011-two-stage, Project ID278742 EUROSARC). DGD and LHP are supported by Red Temática de Investigación Cooperativa en Cáncer (RD12/0036/0017) and Centro de Investigación Biomédica en Red de Cáncer (CB16/12/00361)S. PRN is supported by a grant from the María García Estrada Foundation. DGD is a PhD researcher funded by the Consejería de Salud, Junta de Andalucía (PI-0197-2016). MJR is supported by the Consejería de Salud, Junta de Andalucía (ECAIF2-0176-2013).

© 2020 by the authors. Ewing sarcoma is a highly aggressive round cell mesenchymal neoplasm, most often occurring in children and young adults. At the molecular level, it is characterized by the presence of recurrent chromosomal translocations. In the last years, next-generation technologies have contributed to a more accurate diagnosis and a refined classification. Moreover, the application of these novel technologies has highlighted the relevance of intertumoral and intratumoral molecular heterogeneity and secondary genetic alterations. Furthermore, they have shown evidence that genomic features can change as the tumor disseminates and are influenced by treatment as well. Similarly, next-generation technologies applied to liquid biopsies will significantly impact patient management by allowing the early detection of relapse and monitoring response to treatment. Finally, the use of these novel technologies has provided data of great value in order to discover new druggable pathways. Thus, this review provides concise updates on the latest progress of these breakthrough technologies, underscoring their importance in the generation of key knowledge, prognosis, and potential treatment of Ewing Sarcoma. This work was supported by grants from the Consejería de Salud (Junta de Andalucía, grants No PI-0036-2017 and PI-0040-2017) awarded to JDM and ATA, respectively; by grants from the Asociación Pablo Ugarte, Fundación María García Estrada and FARO niños con cáncer to JDM and EdA. EdA’s laboratory is supported by the AECC project (GCB13-1578), ISCIIIFEDER (PI14/01466, PI17/00464), CIBERONC (CB16/12/00361) and Fundación CRIS Contra el Cáncer. This work was also supported by a Juan de la Cierva Incorporación fellowship (IJC-2018-036767-I) to ATA, and a pre-doctoral fellowship from the VI Plan Propio from the Universidad de Sevilla to JOP.

Ewing sarcoma is a bone and soft tissue tumor predominantly affecting adolescents and young adults. To characterize changes in anticancer drug activity and intratumor drug distribution during the evolution of Ewing sarcomas, we used immunodeficient mice to establish pairs of patient-derived xenografts (PDX) at early (initial diagnosis) and late (relapse or refractory progression) stages of the disease from three patients. Analysis of copy number alterations (CNA) in early passage PDX tissues showed that two tumor pairs established from patients which responded initially to therapy and relapsed more than one year later displayed similar CNAs at early and late stages. For these two patients, PDX established from late tumors were more resistant to chemotherapy (irinotecan) than early counterparts. In contrast, the tumor pair established at refractory progression showed highly dissimilar CNA profiles, and the pattern of response to chemotherapy was discordant with those of relapsed cases. In mice receiving irinotecan infusions, the level of SN-38 (active metabolite of irinotecan) in the intracellular tumor compartment was reduced in tumors at later stages compared to earlier tumors for those pairs bearing similar CNAs, suggesting that distribution of anticancer drug shifted toward the extracellular compartment during clonal tumor evolution. Overexpression of the drug transporter P-glycoprotein in late tumor was likely responsible for this shift in drug distribution in one of the cases., The work at Hospital Sant Joan de Deu was supported by associations of parents and families of children with cancer. The work of EdA was supported by the AECC Scientific Foundation (GCB13-1578), ISCIII-FEDER (PI14/01466 and PI17/00464), CIBERONC (CB16/12/00361), Asociación Pablo Ugarte and Fundación María García Estrada. The work of JM was supported by the AECC Scientific Foundation (GCB13-1578) and Asociación Pablo Ugarte. The work of AMC was supported by grants from the AECC Scientific Foundation, MINECO (SAF2011-22660), Fundacion BBVA (152/2011), the European Union Seventh Framework Programme (FP7/2007-2013) under Marie Curie International Reintegration Grant (PIRG-08-GA-2010-276998) and ISCIII-FEDER (CP13/00189 and CPII18/00009).

Chemotherapy is one of the most established and effective treatments for almost all types of cancer. However, the elevated toxicity due to the non-tumor-associated effects, development of secondary malignancies, infertility, radiation-induced fibrosis and resistance to treatment limit the effectiveness and safety of treatment. In addition, these multiple factors significantly impact quality of life. Over the last decades, our increased understanding of cancer epigenetics has led to new therapeutic approaches and the promise of improved patient outcomes. Epigenetic alterations are commonly found in cancer, especially the increased expression and activity of histone deacetylases (HDACs). Dysregulation of HDACs are critical to the development and progression of the majority of tumors. Hence, HDACs inhibitors (HDACis) were developed and now represent a very promising treatment strategy. The use of HDACis as monotherapy has shown very positive pre-clinical results, but clinical trials have had only limited success. However, combinatorial regimens with other cancer drugs have shown synergistic effects both in pre-clinical and clinical studies. At the same time, these combinations have enhanced the efficacy, reduced the toxicity and tumor resistance to therapy. In this review, we will examine examples of HDACis used in combination with other cancer drugs and highlight the synergistic effects observed in recent preclinical and clinical studies. This work was supported by Instituto de Salud Carlos III_FEDER (PI17/00464 and CB16/12/00361), by the Consejería de Salud, Junta de Andalucía (PI-0013-2018), and by Fundación María García Estrada.

Ewing sarcoma is the second most frequent bone tumour of childhood and adolescence that can also arise in soft tissue. Ewing sarcoma is a highly aggressive cancer, with a survival of 70–80% for patients with standard-risk and localized disease and ~30% for those with metastatic disease. Treatment comprises local surgery, radiotherapy and polychemotherapy, which are associated with acute and chronic adverse effects that may compromise quality of life in survivors. Histologically, Ewing sarcomas are composed of small round cells expressing high levels of CD99. Genetically, they are characterized by balanced chromosomal translocations in which a member of the FET gene family is fused with an ETS transcription factor, with the most common fusion being EWSR1–FLI1 (85% of cases). Ewing sarcoma breakpoint region 1 protein (EWSR1)–Friend leukaemia integration 1 transcription factor (FLI1) is a tumour-specific chimeric transcription factor (EWSR1–FLI1) with neomorphic effects that massively rewires the transcriptome. Additionally, EWSR1–FLI1 reprogrammes the epigenome by inducing de novo enhancers at GGAA microsatellites and by altering the state of gene regulatory elements, creating a unique epigenetic signature. Additional mutations at diagnosis are rare and mainly involve STAG2, TP53 and CDKN2A deletions. Emerging studies on the molecular mechanisms of Ewing sarcoma hold promise for improvements in early detection, disease monitoring, lower treatment-related toxicity, overall survival and quality of life. T.G.P.G. is supported by grants from the Wilhelm Sander Foundation (2016.167.1), German Cancer Aid (DKH-111886 and DKH-70112257) and the Deutsche Forschungsgemeinschaft (DFG 391665916). F.C.-A. is supported by a grant from the Barbara and Hubertus Trettner Foundation. E.M.T. is supported by a fellowship from the Austrian Science Fund (FWF; Elise Richter Fellowship V506-B28). E.d.A. is supported by grants from the Spanish Ministry of Economy-FEDER (PI17/00464, CB16/12/00361), the Asociación Pablo Ugarte and the María García-Estrada Foundation. U.D. is supported by grants from the German Cancer Aid (DKH108128 and DKH 70112018); ERA-Net-TRANSCAN (01KT1310), EEC, EU-FP7 602856, Trettner Foundation and Stiftung für krebskranke Kinder in Essen.

Ewing sarcoma is the second most frequent bone tumour of childhood and adolescence that can also arise in soft tissue. Ewing sarcoma is a highly aggressive cancer, with a survival of 70–80% for patients with standard-risk and localized disease and ~30% for those with metastatic disease. Treatment comprises local surgery, radiotherapy and polychemotherapy, which are associated with acute and chronic adverse effects that may compromise quality of life in survivors. Histologically, Ewing sarcomas are composed of small round cells expressing high levels of CD99. Genetically, they are characterized by balanced chromosomal translocations in which a member of the FET gene family is fused with an ETS transcription factor, with the most common fusion being EWSR1–FLI1 (85% of cases). Ewing sarcoma breakpoint region 1 protein (EWSR1)–Friend leukaemia integration 1 transcription factor (FLI1) is a tumour-specific chimeric transcription factor (EWSR1–FLI1) with neomorphic effects that massively rewires the transcriptome. Additionally, EWSR1–FLI1 reprogrammes the epigenome by inducing de novo enhancers at GGAA microsatellites and by altering the state of gene regulatory elements, creating a unique epigenetic signature. Additional mutations at diagnosis are rare and mainly involve STAG2, TP53 and CDKN2A deletions. Emerging studies on the molecular mechanisms of Ewing sarcoma hold promise for improvements in early detection, disease monitoring, lower treatment-related toxicity, overall survival and quality of life., T.G.P.G. is supported by grants from the Wilhelm Sander Foundation (2016.167.1), German Cancer Aid (DKH-111886 and DKH-70112257) and the Deutsche Forschungsgemeinschaft (DFG 391665916). F.C.-A. is supported by a grant from the Barbara and Hubertus Trettner Foundation. E.M.T. is supported by a fellowship from the Austrian Science Fund (FWF; Elise Richter Fellowship V506-B28). E.d.A. is supported by grants from the Spanish Ministry of Economy-FEDER (PI17/00464, CB16/12/00361), the Asociación Pablo Ugarte and the María García-Estrada Foundation. U.D. is supported by grants from the German Cancer Aid (DKH108128 and DKH 70112018); ERA-Net-TRANSCAN (01KT1310), EEC, EU-FP7 602856, Trettner Foundation and Stiftung für krebskranke Kinder in Essen.

Wilms tumour (WT) is the most common renal tumour in children. Most WT patients respond to chemotherapy, but subsets of tumours develop resistance to chemotherapeutic agents, which is a major obstacle in their successful treatment. Multidrug resistance transporters play a crucial role in the development of resistance in cancer due to the efflux of anticancer agents out of cells. The aim of this study was to explore several human multidrug resistance transporters in 46 WT and 40 non-neoplastic control tissues (normal kidney) from patients selected after chemotherapy treatment SIOP 93–01, SIOP 2001. Our data showed that the majority of the studied multidrug resistance transporters were downregulated or unchanged between tumours and control tissues. However, BCRP1, MDR3 and MRP1 were upregulated in tumours versus control tissues. MDR3 and MRP1 overexpression correlated with high-risk tumours (SIOP classification) (p = 0.0022 and p < 0.0001, respectively) and the time of disease-free survival was significantly shorter in patients with high transcript levels of MDR3 (p = 0.0359). MDR3 and MRP1 play a role in drug resistance in WT treatment, probably by alteration of an unspecific drug excretion system. Besides, within the blastemal subtype, we observed patients with low MDR3 expression were significantly associated with a better outcome than patients with high MDR3 expression. We could define two types of blastemal WT associated with different disease outcomes, enabling the stratification of blastemal WT patients based on the expression levels of the multidrug resistance transporter MDR3., LHP and DJGD are supported by Red Temática de Investigación Cooperativa en Cáncer (RD12/0036/0017). CS was supported by a contract from Nicolás Monardes Program, Consejería de Salud, Junta de Andalucía. Research in Enrique de Alava’s lab is also supported by the Ministry of Economy and Competitiveness of Spain-FEDER (PI1401466, RD06/0020/0059, PI1100018, ISCIII postdoc grant CD06/00001), María García-Estrada Foundation and the European Commission (FP7-HEALTH-2011-two-stage, Project ID 278742 EUROSARC). Research in Carmen Sáez lab is also supported by research grants from the Instituto de Salud Carlos III, FIS PI13/02282.