Activation of myc gene family in human lung carcinomas and during heterotransplantation into nude mice.

myc gene family activation (c-myc, L-myc, and N-myc) was examined in 26 human lung carcinomas and in their corresponding xenografts in nude mice. Of the 16 neuroendocrine (NE) carcinomas studied, amplification was observed in 4 with a c-myc probe and in 1 with both L- and N-myc probes. Overexpression was found in 1 of 7 cases studied for c-myc mRNA, in 1 of 7 cases for N-myc, and in 2 of 7 cases for L-myc. Of the 10 non-small cell lung carcinomas studied, only c-myc was amplified in 1 case and overexpressed in 5 of 7 cases. These results suggest that L- and N-myc gene activation are restricted to NE carcinomas. Over-expression of the myc gene without amplification was detected in 36% of cases. During heterotransplantation, there was a 27% change in myc gene abnormality and a 57% increase in myc expression levels, mostly in NE carcinomas (5 of 7; 71%). In a total of 42 xenografted lung carcinomas studied, 45% amplification and 77% overexpression of one of the myc genes were detected with a high prevalence of L-myc overexpression in NE carcinomas (50%) and of c-myc overexpression in non-small cell lung carcinomas (66%). Finally, 19 of 26 (73%) tumors are growing in nude mice with no myc gene amplification and 43% with no myc mRNA overexpression. Thus myc gene activation is not strictly required for heterotransplantation but seems to be a favorable factor in the maintenance and progression of lung carcinomas in vivo.