Highly sensitive analysis for N-myc amplification in neuroblastoma based on fluorescence in situ hybridization

Background/Purpose: The N-myc amplification status in neuroblastoma has been evaluated previously for the whole tumor by the Southern blot method. The aim of this study is to evaluate the effectiveness of the fluorescence in situ hybridization (FISH) method to analyze N-myc amplification in neuroblastoma and compare the findings with those using the Southern blot method. Methods: In 26 neuroblastoma primary tumors and metastatic lesions, the N-myc amplification status was evaluated by both the Southern blot method and FISH method. Results: Of the 22 samples with no N-myc amplification using Southern blot, no cells with N-myc amplification using FISH were present in 21 of the samples. However, one metastatic liver lesion showed 16% of the nuclei to display more than 10 copies of N-myc based on FISH analysis. In the 4 remaining samples with N-myc amplification using the Southern blot method (17 copies, 15 copies, 6 copies, and 3 copies), the rates of cells with more than 10 copies of N-myc based on a FISH analysis were 79%, 68%, 94%, and 9%, respectively. Conclusions: The FISH method can detect more accurately N-myc amplification than the Southern blot method either when the rate of cells with N-myc amplification is low or intratumor heterogeneity is present.