Clinical Significance of Liquid Biopsy Analysis in Pediatric Sarcoma Patients

Sarcomas are aggressive pediatric tumors of mesenchymal origin that arise in bones and soft tissues. In the majority of cases, sarcomas that occur in childhood and adolescence are osteosarcoma (OS), Ewing sarcoma (EWS) and rhabdomyosarcoma (RMS). Although survival of patients with localized disease at diagnosis has improved over the years, the prognosis for those who relapse or develop metastases is still dismal. Nowadays, hence, there is an unmet need for novel biomarkers able to identify non-responder patients and patients at high risk of relapse. The aim of my Ph.D. was to discover and investigate the clinical utility of new blood-based biomarkers for children and adolescents with sarcomas, specifically circulating tumor DNA (ctDNA) and tumor-associated autoantibodies (TAABs). By performing targeted sequencing of circulating cell-free DNA, I've detected and identified somatic alterations of the ctDNA collected at diagnosis and relapse in the blood of pediatric patients with various sarcoma types. Some somatic alterations were selected, validated and tracked longitudinally in samples collected during therapy and at follow-up in order to assess the utility of ctDNA in monitoring patients’ response or resistance to therapy. On the other hand, high-density protein microarrays capable of detecting the presence of autoantibodies directed against potential tumor antigens were used together with EWS patients' plasma samples. By doing so, I've defined for the first time the antibody profile of children with Ewing sarcoma. Some EWS-associated antibodies were selected, validated, and evaluated as diagnostic and prognostic disease biomarkers. Moreover, since the relapse rate is high in EWS patients and usually leads to a negative outcome, I've compared the antibody profile at diagnosis in patients who achieved clinical remission without occurrence of events and those who had rapid relapse. In conclusion, using high-throughput approaches I've characterized both circulating ctDNA and TAABs as new potential biomarkers for children and adolescents with sarcomas, confirmed any obtained result with independent techniques, and tested their validity as suitable biomarkers for clinical usage.