 molecular markers such as mutational spectra or mrna expression patterns may give some indication of the mechanisms of carcinogenesis induced by fibers and other carcinogens . in our study , tumors were induced by application of crocidolite asbestos or benzo[a]pyrene ( b[a]p ) to rat peritoneum . 
 dna and rna of these tumors were subjected to analysis of point mutations and to investigation of mrna expression patterns . with both assays we found typical features depending on the type of carcinogen applied . 
 the analysis of point mutations in the tumor suppressor gene p53 revealed mutations in the b[a]p - induced tumors . 
 however , in the tumors induced by crocidolite asbestos that were of the same tumor type as those induced by b[a]p , mutations in p53 were not detectable . every mutation detected on the dna level causes an amino acid substitution within one of the functional domains of the tumor suppressor protein . 
 therefore , these mutations seem to be of biological relevance for tumor progression and indicate a difference in the carcinogenesis regarding the type of the carcinogenic substance . an additional specificity of crocidolite - induced tumors was detectable by analyzing the mrna expression of the tumor suppressor gene wt1 , which is known to be expressed in human mesothelial and mesothelioma cells . 
 a relatively high amount of wt1 mrna was measured by quantitative competitive reverse transcription - polymerase using rna extracted from crocidolite - induced tumors . 
 however , wt1 seems to be expressed on a rather low level in tumors induced by b[a]p.imagesfigure 1.figure 2.figure 2.figure 2.figure 2 . 
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