 we studied the prevalence of point mutations in ras oncogenes ( k - ras and n - ras ) in dna from white blood cells and tumor tissue from 36 untreated patients with non - small - cell lung cancer , all of whom were smokers or ex - smokers . 
 we observed somatic k - ras mutations in one - third of the lung carcinomas studied but no n - ras mutation . 
 k - ras codon 12 mutations were found more frequently in adenocarcinomas than in the other histopathological subtypes studied . 
 more than 60% ( 10/16 ) of the lung adenocarcinomas had a codon 12 mutation , most of which were g to t transversions . 
 no mutations was found in white blood cell dna . 
 two polymerase chain reaction screening methods , oligonucleotide hybridization and denaturing gradient gel electrophoresis ( dgge ) , were used to detect the mutations . 
 the oligonucleotide method appears to be more sensitive than dgge , but dgge proved to be a reliable nonradioactive method for rapid screening of point mutations in genes relevant to carcinogenesis.imagesfigure 1 . 
 afigure 1 . 
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