Forty-two cases of squamous cell carcinoma arising in the upper aerodigestive tract were examined to determine the incidence and type of point mutation in codon 12 of the c-K-ras gene by using the polymerase chain reaction and oligonucleotide hybridization techniques on DNA extracted from paraffin blocks.
By NIH3T3 transfection assay in conjunction with in vitro transient neomycin selection, activated c-H-ras-1 oncogenes were detected in two squamous cell carcinoma cell lines, ZA and HOC-313, newly established from human oral cancer patients.
This investigation of oral squamous carcinoma in five individuals revealed that four of the patients were constitutionally heterozygous at the c-Ha-ras-1 locus and that the tumour from one patient had lost that heterozygosity.
Interestingly, DNA from both primary and secondary transformants of one particular human squamous cell carcinoma contained highly amplified copies of the Ha-ras oncogene.