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 bladd er tumors selected on the basis of high grade and/or p53 overexpression (im munohistochemistry without antigen retrieval). Fourteen point mutations in 13 tumors and one 21 bp deletion in another tumor were identified. In addit ion, a germ-line mutation corresponding to a previously described polymorph ism was detected in exon 6, in two tumors. Mostly G-->A transitions (10) we re found. Only three occurred at CPG sites, suggesting a major role for exo genous carcinogens in bladder tumorigenesis, Immunostaining for p53 and MDM 2, using antigen retrieval, was carried out on the same tumors. A correlati on was found between the percentage of p53-positive cells and the presence of p53 mutations (P = 0.005). No correlation was found between overexpressi on 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 h abits of the patients, A significant association was found between the pres ence 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 s moked for greater than or equal to 30 years and if former smokers, had stop ped for less than or equal to 5 years. However, no correlation was found be tween the presence of p53 point mutations and the number of cigarettes smok ed. The deletion mutation was the only one present in a tumor from a non-sm oker, The data suggest that duration of exposure to carcinogens is the most critical factor in p53 mutagenesis in bladder cancer.