Level of Seven Neuroblastoma-Associated mRNAs Detected by Droplet Digital PCR Is Associated with Tumor Relapse/Regrowth of High-Risk Neuroblastoma Patients.

Monitoring of several sets of neuroblastoma-associated mRNAs (NB-mRNAs) by real-time quantitative PCR (qPCR) can be used to evaluate minimal residual disease in NB patients. Droplet digital PCR (ddPCR) is an adaption of qPCR that potentially provides simpler and more reproducible detection of low levels of mRNAs. However, whether minimal residual disease in NB patients can be monitored by ddPCR using a set of NB-mRNAs is not yet tested. In this study, 208 bone marrow (BM) and 67 peripheral blood samples were retrospectively collected from 20 high-risk NB patients with clinical disease evaluation at two Japanese centers between 2011 and 2018, and level of each NB-mRNA (CRMP1, DBH, DDC, GAP43, ISL1, PHOX2B, and TH mRNAs) was determined by ddPCR. Level of 7NB-mRNAs (defined as the combined signature of each NB-mRNA) was higher in BM than peripheral blood, but correlated significantly with each other. In accordance with disease burden, it varied with disease status (remission, stable, or progression) and collection time point (diagnosis, treatment, post-treatment, or relapse). In 73 post-treatment BM samples, it was significantly higher in 17 relapsed/regrown samples than in 56 nonrelapsed/nonregrown samples. Furthermore, ddPCR had a better prognostic value than qPCR in detecting 7NB-mRNAs in the same 73 post-treatment BM samples. This study suggests that ddPCR detection of 7NB-mRNAs is significantly associated with tumor relapse/regrowth in high-risk NB patients.