Introduction. Circulating tumor DNA (ctDNA) has been used for disease monitoring in several types of cancer. Therefore, the aim of our study was to investigate whether ctDNA can be used for treatment response monitoring in neuroblastoma.
Method 121 plasma samples from 50 patients were analyzed for the detection of hypermethylated RASSF1A DNA. DNA was isolated and total cell free DNA (cfDNA) was determined by qPCR for albumin and the amount of ctDNA was determined by qPCR for methylated RASSF1A after bisulfite conversion. Detection of ctDNA was compared with clinic-biological patient characteristics, such as BM and PB MRD (qPCR), MIBG scans and urinary catecholamines.
Results In 13/20 diagnostic samples ctDNA was detected. In all 7 diagnostic samples from patients with localized disease no ctDNA was detected. During induction chemotherapy (stage 4 patients only) in 13/42 samples ctDNA was detected (30%). At relapse in 8 out of 14 samples ctDNA was detected (57%). The amount of cfDNA was significantly higher in neuroblastoma patient at time of diagnosis and relapse than in healthy controls and stage 4 patients had the highest amount of cfDNA. There was a significant correlation between ctDNA and PB or BM MRD, when tumor levels were high or no tumor was detected. Discrepancies were observed in 20 samples and were studied in detail. The discrepancies were mainly observed in samples during treatment when tumor burden was lower.
Conclusion Hypermethylated RASSF1A can be used as marker for monitoring of ctDNA in neuroblastoma patients and highly correlates with the disease status at diagnosis. Our data indicate that there is no correlation when tumor load is lower because during treatment in several samples discrepancies were observed. It is likely that ctDNA can originate from both primary tumor as metastases and may be of special interest for disease monitoring in patients relapsing in other organs than the BM.