Identificazione e validazione di biomarcatori molecolari nel sarcoma di Ewing

Ewing sarcoma, the second most common primary bone malignancy, is a highly aggressive mesenchymal tumor arising mainly in adolescents and young adults. Current multimodal treatment has reached a plateau of 70% 5-year overall survival (5y OVS) for patients with localized disease, and 30% and 25% for patients with metastatic or recurrent disease. Moreover, patients often suffer from acute and long term toxicity related to chemotherapy. It is thus paramount the development of molecular biomarkers allowing stratification of patients based on risk at diagnosis. The present study validates LGALS3BP and miR-34a as independent predictors of clinical outcome in 124 Ewing sarcoma patients treated in a single Institution. Patients with high expression levels of these molecules have lower risk of developing local recurrences or metastasis (HR 0.402, 95% CI 0.190-0.850 for LGALS3BP;HR 0.485, 95% CI 0.236 -0.996 for miR-34a), and a lower risk of disease-related death (HR 0.397, 95% CI 0.159- 0.993 for LGALS3BP; HR 0.353, 95% CI 0.132-0.943 for miR-34a). By developing and characterizing in vitro and in vivo a stable miR34a expression model, we confirmed its oncosuppressor role in Ewing sarcoma; one of the underlying mechanisms involve the inhibition of the 1B isoform of cyclin D1, a direct target of EWS-FLI1, the aberrant transcription factor characteristic of the disease. We also show the feasibility of non-invasive circulating miR-34a quantification. Through a whole transcriptome sequencing approach applied to pre-treatment biopsies from patients with differential chemotherapy response, we identified 4 mutations in the TP53 gene (p.R213X, p.R248W, p.R273C and p.K386M de novo mutation) defining a patient group with poor response to treatment, and a panel of lincRNA with differential expression in the two groups. Overall these results contribute to the definition of a spectrum of molecular features of Ewing sarcoma impacting clinical outcome, which are promising candidates for prospective validation.