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Liquid biopsy strategies in pediatric patients are challenging due to low body weight. This study investigated cfDNA size distribution and concentration in blood, bone marrow, cerebrospinal fluid, and urine from 84 patients with neuroblastoma classified as low ( n = 28), intermediate ( n = 6), or high risk ( n = 50) to provide key data for liquid biopsy biobanking strategies. The average volume of blood and bone marrow plasma provided ranged between 1 and 2 mL. Analysis of 637 DNA electropherograms obtained by Agilent TapeStation measurement revealed five different major profiles and characteristic DNA size distribution patterns for each of the biofluids. The proportion of samples containing primarily cfDNA was, at 85.5%, the highest for blood plasma. The median cfDNA concentration amounted to 6.28 ng/mL (blood plasma), 58.2 ng/mL (bone marrow plasma), 0.08 ng/mL (cerebrospinal fluid), and 0.49 ng/mL (urine) in samples. Meta-analysis of the dataset demonstrated that multiple cfDNA-based assays employing the same biofluid sample optimally require sampling volumes of 1 mL for blood and bone marrow plasma, 2 mL for cerebrospinal fluid, and as large as possible for urine samples. A favorable response to treatment was associated with a rapid decrease in blood-based cfDNA concentration in patients with high-risk neuroblastoma. Blood-based cfDNA concentration was not sufficient as a single parameter to indicate high-risk disease recurrence. We provide proof of concept that monitoring neuroblastoma-specific markers in very small blood volumes from infants is feasible.

The invasive nature of surgical biopsies deters sequential application, and single biopsies often fail to reflect tumor dynamics, intratumor heterogeneity and drug sensitivities likely to change during tumor evolution and treatment. Implementing molecular characterization of cell-free neuroblastoma-derived DNA isolated from blood plasma could improve disease assessment for treatment selection and monitoring of patients with high-risk neuroblastoma. We established droplet digital PCR (ddPCR) protocols for MYCN and ALK copy number status in plasma from neuroblastoma patients. Our ddPCR protocol accurately discriminated between MYCN and ALK amplification, gain and normal diploid status in a large panel of neuroblastoma cell lines, and discrepancies with reported MYCN and ALK status were detected, including a high-level MYCN amplification in NB-1, a MYCN gain in SH-SY5Y, a high-level ALK amplification in IMR-32 and ALK gains in BE(2)-C, Kelly, SH-SY5Y and LAN-6. MYCN and ALK status were also reliably determined from cell-free DNA derived from medium conditioned by the cell lines. MYCN and ALK copy numbers of subcutaneous neuroblastoma xenograft tumors were accurately determined from cell-free DNA in the mouse blood plasma. In a final validation step, we accurately distinguished MYCN and ALK copy numbers of the corresponding primary tumors using retrospectively collected blood plasma samples from 10 neuroblastoma patients. Our data justify the further development of molecular disease characterization using cell-free DNA in blood plasma from patients with neuroblastoma. This expanded molecular diagnostic palette may improve monitoring of disease progression including relapse and metastatic events as well as therapy success or failure in high-risk neuroblastoma patients., Competing Interests: CONFLICTS OF INTEREST None.