Purpose: MYCN amplification (MNA) indicates a poor prognosis in neuroblastoma (NB) and is routinely assayed for therapy stratification. We aimed to develop a diagnostic tool to predict MYCN status using serum DNA, which, in cancer patients, predominantly originates from tumor-released DNA.
Patients and 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 an MYCN/NAGK (M/N) ratio in 87 NB patients whose MYCN status had been determined by Southern blotting. Of these patients, 17 had MYCN-amplified NB, and 70 had nonamplified NB.
Results: The serum M/N ratio in the MNA group (median, 199.32; range, 17.1 to 901.6; 99% CI, 107.0 to 528.7) was significantly (P < .001) higher than the ratio in the non-MNA group (median, 0.87; range, 0.25 to 4.6; 99% CI, 0.82 to 1.26; Mann-Whitney U test). The sensitivity and specificity of the serum M/N ratio as a diagnostic test were both 100% when the serum M/N ratio cutoff was set at 10.0. Among six MNA patients whose clinical courses were followed, the serum ratios decreased to the normal range in the patients in remission (n = 3), whereas the ratios increased to high levels in the patients who relapsed (n = 2) or failed to achieve remission (n = 1).
Conclusion: Measurement of the serum M/N ratio seems to be a promising method for accurately assessing MYCN status in NB, although a larger set of patients needs to be examined to confirm this result.