Detection of amplified N-myc gene in neuroblastoma by in situ hybridization using the single-step silver enhancement method

Amplification of the N-myc oncogene in 27 cases of neuroblastoma group tumor was examined by in situ hybridization using the single-step silver enhancement technique. The N-myc gene copy numbers of these neuroblastoma group tumors were previously examined by dot-blot hybridization using DNA extracted from formalin-fixed, paraffin-embedded tissues (H Tsuda et al., Lab Invest, 59:321, 1988). Silver grains were deposited just over the nuclei of tumor cells, but no or only faint deposition was observed over those of infiltrating lymphocytes, stromal fibroblasts, and endothelial cells. We judged a case to be positive for gene amplification when silver grains precipitated over the nuclei of the tumor cells to a greater extent than over nuclei of lymphocytes or endothelial cells in the same section. According to this criterion, 14 cases (12 cases of neuroblastoma and 2 cases of ganglioneuroblastoma) were positive for N-myc gene amplification of 27 cases (18 cases of neuroblastoma, 5 cases of ganglioneuroblastoma, and 4 cases of composite ganglioneuroblastoma). These results corresponded well to those of the dot-blot hybridization analysis using the same materials. Thirteen of 15 cases that carried 4 copies or more of N-myc gene were judged positive, and 11 of 12 cases that carried less than 4 copies of the N-myc gene were judged negative by in situ hybridization. In neuroblastoma group tumors with amplification of the N-myc gene, tumor cells were stained almost homogenously, except for two cases of ganglioneuroblastoma, in which less differentiated small round tumor cells were stained more intensely than differentiated ganglion-like cells.(ABSTRACT TRUNCATED AT 250 WORDS)