Serum Levels Of Mycn Amplification In Neuroblastoma With Tumor-Released Dna By Real-Time Quantitative Polymerase Chain Reaction

INTRODUCTION: MYCN amplification (MNA) indicates a poor prognosis in neuroblastoma and is routinely assayed for therapy stratification. OBJECTIVE: We aimed to develop a diagnostic tool to predict MYCN status by using serum DNA, which, in patients with cancer, predominantly originates from tumor-released DNA. METHODS: Using DNA-based real-time quantitative polymerase chain reaction, we simultaneously quantified MYCN (2p24) and a reference gene, NAGK (2p12), and evaluated MYCN copy number as a MYCN/NAGK ratio in 87 patients with neuroblastoma whose MYCN status had been determined by Southern blotting. Of these patients, 17 had MYCN-amplified neuroblastoma, and 70 had nonamplified neuroblastoma. RESULTS: The serum MYCN/NAGK ratio in the MNA group (median: 199.32; range: 17.1–901.6 [99% confidence interval: 107.0–528.7]) was significantly (P < .001) higher than that in the non-MNA group (median: 0.87; range: 0.25–4.6 [99% confidence interval: 0.82–1.26], Mann-Whitney U test). The sensitivity and specificity of the serum MYCN/NAGK ratio as a diagnostic test were both 100% when the serum MYCN/NAGK ratio cutoff was set at 10.0. Among 6 patients in the MNA group whose clinical courses were followed, the serum ratios decreased to within the normal range in the patients in remission (n = 3), but they rose to high levels in the patients who had a relapse (n = 2) or failed to achieve remission (n = 1). The serum MYCN/NAGK ratio in the MNA group is likely to be the more sensitive tumor marker than conventional urinary vanillylmandelic and homovanillic acid markers and neuron-specific enolase markers to predict patients' clinical course. CONCLUSIONS: Measurement of the serum MYCN/NAGK ratio seems to be a promising method for accurately assessing MYCN status in neuroblastoma.