Comparison of mutations in the p53 and K-ras genes in lung carcinomas from smoking and nonsmoking women

Abstract

Lung cancer incidence is increasing in women with little or no tobacco exposure, and the cause of this trend is not known. One possibility is increased sensitivity to environmental tobacco smoke in women nonsmokers diagnosed with lung cancer. To determine whether mutations associated with tobacco exposure are found in the lung tumors of women who are lifetime nonsmokers or occasional smokers, we compared the p53 and K-ras mutational spectra in lung carcinomas from 23 female nonsmokers, 2 female occasional smokers (< 10 pack-years), and 30 female long-term smokers (20-100 pack-years). We also looked for p53 and K-ras mutations in three carcinoid lung tumors, two from female nonsmokers and one from a female occasional smoker. For the p53 gene, exons 4-8 were examined for mutations; for the K-ras gene, exon 1 was examined. No mutations were found in the carcinoid tumors. In lung carcinomas, p53 mutations were identified in six (26.1%) of the cases from lifetime nonsmokers and consisted of five transitions (including three C to T, one G to A, and one T to C) and one T to A transversion. In comparison, p53 mutations were identified in 10 (31.3%) of the 32 lung carcinomas from short-term and long-term smokers and consisted of six transversions (four G to T, one A to T, and one G to C), one A to G transition, one C to T transition, and two deletions of one to four bp. Mutations in the p53 gene found in nonsmokers also occurred in either different codons or different positions within a codon compared with those seen in long-term smokers. K-ras mutations in codon 12 were identified in two lung carcinomas (8.7%) from lifetime nonsmokers. The K-ras mutations found were a G to T transversion and a G to A transition. Eight (25%) of the 32 lung carcinomas from smokers contained K-ras mutations in codons 12 and 13 (four G to T transversions and four G to A transitions). In addition, six silent mutations that are most likely polymorphisms were found in both smokers and nonsmokers. These results confirm that K-ras mutations are more frequent in smokers than in nonsmokers, but that the same type of mutation in the K-ras gene is found in both groups. In contrast, although the frequency of mutation in the p53 gene was similar in lifetime nonsmokers compared with long-term smokers, the types and spectra of mutation are significantly different. Two of the C to T transitions found in nonsmokers, but none of those found in smokers, occur at the C of a CpG site. These results suggest the mutagen(s) and/or mechanisms of p53 mutations in women nonsmokers are different from those responsible for p53 mutations in women smokers, which are probably largely induced by tobacco mutagens.