Increased Expression of ras Genes in Non‐Hodgkin's Lymphomas Is not Associated with Oncogenic Activation of Those Genes by Point Mutation

Twenty‐three cases of non‐Hodgkin's lymphoma (NHL) were analyzed for expression of ras genes by in situ hybridization utilizing biotinylated DNA probes. Increased expression of Ki‐ras, Ha‐ras and N‐ras genes was observed in 12 cases, 6 cases and 1 case of NHL, respectively. Genomic DNA extracted from these 23 cases of NHL was region‐specifically amplified by means of polymerase chain reaction to examine the presence of point mutations at the 12th, 13th and 61st codons of Ki‐, Ha‐ and N‐ras genes. Dot hybridization assays with appropriate oligonucleotide probes showed no evidence of point mutation in any case of NHL examined. These results indicate that increased expression of ras genes in NHL is not associated with ras gene activation by point mutation.