Feasibility of tumor-informed circulating tumor DNA (ctDNA) for molecular residual disease (MRD) assessment in pediatric patients with solid tumors.

10058 Background: Circulating Tumor DNA (ctDNA) is a noninvasive biomarker which has been validated as a prognostic tool in multiple adult cancers. There is evolving evidence that ctDNA may be prognostic in pediatric solid tumors, but experience with commercially available assays in pediatric patients is scarce. Signatera is a ctDNA assay which utilizes whole exome sequencing of tumor and whole blood to identify 16 tumor-specific, clonal, somatic variants. These variants are then monitored in plasma as a molecular residual disease (MRD) assessment. Methods: From November 2021 through August 2023, 30 patients were enrolled on a single center study evaluating the feasibility and utility of Signatera MRD monitoring in pediatric patients with solid tumors. Patients 6 months to 25 years of age with any malignant extracranial solid tumor including lymphoma were eligible. Peripheral blood has been collected every 3 weeks to 3 months while on therapy and every 3 to 6 months while off therapy for up to 2 years. A minimum of 22mL of blood was required for the first draw, and 16mL for subsequent draws. Timing of blood draws was aligned with standard of care blood draws when possible. Results of ctDNA MRD were compared with imaging obtained for disease response and surveillance as standard of care. Results: The cohort consisted of 6 cases of neuroblastoma, 6 osteosarcomas, 4 Wilms tumors, 4 carcinomas, 3 soft tissue sarcomas, 2 Ewing sarcomas, 2 germ cell tumors, 2 lymphomas, and one hepatoblastoma. Of 30 patients enrolled, a tumor-informed ctDNA assay was successfully created for 27 (90%). Of 25 patients who had radiographic evidence of disease at any time of monitoring, 23 (92%) had simultaneous detectable ctDNA. Seven patients have had disease recurrence, of whom all seven had detectable ctDNA at or preceding time of recurrence. Conclusions: Signatera tumor-informed ctDNA assay is a feasible noninvasive tool which may be utilized in parallel with standard of care imaging to monitor for disease recurrence in pediatric patients with extracranial solid tumors. Additional analysis of a larger patient cohort is needed to identify tumor types and clinical scenarios for which its application is most useful.