Histologic-genetic mapping of cystectomy specimens in bladder cancer patients reveals frequent genetic alterations in dysplastic and histologically normal urothelium

R Stoehr, BS,a, R Knuechel-Clarke, MD,a, R Schmitt, PhD,b, F Hofstaedter, MD, a, A Hartmann, MD, a

aInstitute of Pathology, University of Regensburg, Germany bDepartment of Genetics, University of Regensburg, Germany

AIM: Most invasive carcinomas of the urinary bladder are associated with extensive precursor lesions in adjacent urothelial areas ranging from mild dysplasia to carcinoma in situ. Limited available data on genetic alterations in these precancerous lesions were the base for our studies of such alterations in multiple areas of cystectomy specimens with invasive urothelial carcinoma, including correlation to histopathological parameters. Methods: 69 samples from 3 cystectomy specimens (fresh from the operating room) were removed and snap-frozen. After diagnosis and microdissection of the urothelium (PALM), loss of heterozygosity (LOH) of 10 polymorphic markers on chromosomes 8p, 9p, 9q and 17p was determined in all specimens. Additionally, exons 5-9 of the p53 gene were investigated for mutations in the invasive cancers and all samples were screened for the specific p53 mutation using allele-specific PCR (PASA). RESULTS: There was an increasing LOH with increasing degree of pre-neoplasia (ranging from 5,3%-18,6% in normal urothelium to 44,4%-88,9% in carcinoma in situ). LOH on different markers on chromosomes 8p, 9p and 9q could already be detected in normal urothelium. Three p53 mutations were discovered in three carcinomas (pT1G3: codon 161, Cis: codon 168, pT1G3: codon 258). PASA revealed patches of histologically normal urothelium containing the specific p53 mutation in all three cystectomy specimens. CONCLUSIONS: 1. Histologic genetic bladder-mapping is a valuable tool to detect early genetic alterations in the development of urothelial carcinomas, 2. Alterations of chromosomes 8 and 9 are frequently present in histologically normal urothelium, 3. Specific p53 mutations are detected in patches of normal urothelium suggesting early spread of tumor cells with p53 mutations by intraluminal seeding, 4. The investigation of more chromosomal regions by LOH and the combination of histologic mapping with CGH and expression analyses could reveal the sequence of specific genetic alterations in urothelial carcinogenesis.

KEY WORDS: Bladder cancer, p53, Histologic bladder mapping.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Molecular Pathology.