Molecular Genetics of Ewing Sarcoma

Ewing sarcoma (ES) is an aggressive tumour affecting mainly children and young adults. When metastases are detected, the survival rate is compromised as a result of a lack of appropriated treatments. Balanced chromosomal translocations, present in all primary ES, originate gene fusions, such as EWSR1-FLI1, which act as aberrant transcription factors. Targeting EWSR1-FLI1 by using RNA interference approaches reduced tumour growth and tumourigenicity of ES cells in vitro and in vivo and is a good tool in order to get knowledge in the ES biology. However, possibility of taking RNA interference into clinic is limited. At present, some drugs affecting gene fusion activity have been reported to reduce tumour growth. In addition, several approaches targeting ES genetic alterations not related to gene fusions or their genetic targets have been recently reported. The use of more appropriated animal models and the study of ES tumour microenvironment and epigenetics will unveil new therapeutic targets. Key Concepts ES is an aggressive developmental tumour. Balanced chromosomal translocation and associated gene fusions are the primary molecular event in ES. Secondary molecular events in ES can define new therapeutic targets and new prognostic markers. The role played by epigenetics in ES and the regulation of chromatin remodelling is beginning to be known. Detection of ES circulating cells or identification of gene expression profiles in peripheral blood cells could become good prognostic markers. Identification of new markers of cancer stem cells could help improve ES therapy. Endoglin could be a relevant therapeutic target in ES. Osteolysis and bone remodelling are important mechanisms of ES tumour growth. ES cells secrete extracellular vesicles, containing aberrant EWSR1-FLI1 mRNA and other growth factors, which interact with surrounding tumour cells and extracellular matrix components. Combination therapy of a dual inhibitor of IGF1R and IR pathways and a DNA damage agent can avoid resistance to IGF1R inhibitors. At present, there is a lack of appropriate genetically engineered mice (GEM) of ES. Keywords: Ewing sarcoma; tumour microenvironment; exosome; endoglin; animal model; epigenetic