Introduction Not all neuroblastoma patients that relapse can be recognized by PCR-based monitoring of bone marrow (BM) and peripheral blood (PB). Because epithelial to mesenchymal transition (EMT) is shown to be involved in tumor progression and therapy resistance and it also has recently been demonstrated that neuroblastoma consists of neuroepithelial (NE) and mesenchymal (MES) cells, the aim of this study was to identify MRD markers that can specifically detect MES-neuroblastoma cells and to study the dynamics of these markers during treatment.
Methods Microarray data were used to identify genes differentially expressed between NE and MES neuroblastoma cell lines. This was followed by extensive RQ-PCR testing in cell lines, control BM, PB, PBSCs and cell subsets. After selecting a specific panel of markers several serial PB, PBSC and BM samples from high risk neuroblastoma patients were tested. Detection of MES RNA markers was compared with NE RNA markers. For a cohort of patients PBSC samples were tested and survival analyses were performed.
Results PRRX1, POSTN and FMO3 were selected as marker panel for the detection of MES NB cells. MES mRNA was not frequently detected in PB samples. However, MES mRNA was frequently detected in PBSC samples and was associated with a poor event free survival. In 95 serial BM samples from 13 patients in complete remission and 16 relapse patients MES RNA markers showed different dynamics during treatment compared to NE RNA markers. Furthermore, MES mRNA was more frequently detected in BM samples from relapse patients (53%) than in BM from patients in CR (32%) (p=0.03).
Conclusion We propose to use POSTN, PRRX1 and FMO3 as marker panel for the detection of MES neuroblastoma cells in PB, BM and PBSCs in neuroblastoma patients. MES markers show different dynamics during treatment and are more frequently positive in patients with adverse outcome. To study the clinical significance these markers should be used alongside the current MRD markers in large prospective studies.