p53 point mutations in initial superficial bladder cancer occur only in tumors from current or recent cigarette smokers

Sequencing of p53 exons 5-8 was carried out on 51 initial superficial bladder tumors selected on the basis of high grade and/or p53 overexpression (immunohistochemistry without antigen retrieval). Fourteen point mutations in 13 tumors and one 21 bp deletion in another tumor were identified. In addition, a germ-line mutation corresponding to a previously described polymorphism was detected in exon 6, in two tumors. Mostly G-->A transitions (10) were found. Only three occurred at CPG sites, suggesting a major role for exogenous carcinogens in bladder tumorigenesis, Immunostaining for p53 and MDM2, using antigen retrieval, was carried out on the same tumors. A correlation was found between the percentage of p53-positive cells and the presence of p53 mutations (P = 0.005). No correlation was found between overexpression of p53 and MDM2 in this selected cohort of mostly high grade tumors. The presence of p53 mutations was also analyzed as a function of the smoking habits of the patients, A significant association was found between the presence of p53 point mutations and the number of years of smoking (P = 0.043). All patients with tumors carrying missense or nonsense p53 mutations had smoked for greater than or equal to 30 years and if former smokers, had stopped for less than or equal to 5 years. However, no correlation was found between the presence of p53 point mutations and the number of cigarettes smoked. The deletion mutation was the only one present in a tumor from a non-smoker, The data suggest that duration of exposure to carcinogens is the most critical factor in p53 mutagenesis in bladder cancer.