Enhanced expression of N-myc messenger RNA in neuroblastomas found by massscreening

A substantial fraction of neuroblastomas found by mass screening have been suggested to regress spontaneously because of the high incidence of infanti le neuroblastomas in the screening population. In this study, 70 neuroblast omas were analyzed for expression of proto-oncogenes related to neuronal di fferentiation to clarify the biological significance of proto-oncogene expr ession in the screening-positive and -negative tumors. The tumors consisted of 39 neuroblastomas found by screening (group 1), 16 non-N-myc-amplified nenroblastomas found by clinical symptom(s) (group 2), and 15 N-myc-amplifi ed neuroblastomas found by clinical symptom(s) (group 3), The expression of c-spc, trk A, and N-myc in tumor tissues was analyzed by quantitative RNA PCR, Neuronal c-srcN2 expression varied significantly in the following orde r: group 1 > group 2 > group 3, The level of expression of trk A was marked ly reduced in group 3 but did not differ in groups 1 and 2, Most tumors in group 3 overexpressed N-myc, However, N-myc expression in group 1 was signi ficantly higher than that in group 2, Thus, the characteristics of proto-on cogene expression in screening-positive tumors included enhanced expression of c-srcN2 and N-myc mRNA, regardless of nonamplification of N-myc, Our re sults suggest that the role of N-myc differs in neuroblastomas detected by screening and in N-myc-amplified tumors.