p53 mutational spectra are different between squamous-cell carcinomas of the lip and the oral cavity

We studied the p53 mutational spectra of 34 lip and 60 intra-oral squamous-cell carcinomas and examined possible etiological and prognostic correlations for these tumor sites. For the p53 analysis of exons 5-8, we used PCR/TGGE screening followed by DNA sequencing. Mutations were found in 18/34 (53%) lip and 22/60 (38%) intra-oral carcinomas. The p53 mutational spectrum of the intra-oral carcinomas comprised transitions and transversions in nearly equal frequency (11 to 10). In comparison, transitions were 3.5 times more frequent than transversions (14 to 4) in carcinomas of the lip. The predominant types of base change found in intra-oral tumors were G:C-to-T:A transversions and G:C-to-A:T transitions (32% each), while in lip tumors G:C-to-A:T transitions (70%) were the most frequent. The rate of lip tumors with mutations was higher in non-smokers (8/13) than in smokers (9/20). In contrast, p53 mutations in intra-oral tumors clustered in smokers (18/47 vs. 2/10). G:C-to-T:A transversions, regarded as tobacco smoke-associated in lung cancer, were found in 2 moderate and 4 heavy smokers with intra-oral cancer. This base substitution was found in none of our lip cancers. In lip tumors, a high rate of mutations occurred at dipyridine sites (13/18); among these were 8 C-to-T transitions and 1 CC-to-TT tandem base transition. These changes are characteristic of DNA damage caused by UV light. The presence of mutational events at the DNA-binding surface of the p53 protein may correlate with poor clinical outcome. However, we could not find any statistically significant correlations between p53 status and survival. Only the recurrence-free interval was significantly shortened in cases with mutations affecting residues of the DNA-binding surface of the p53 protein.