Molecular evolution and intratumor heterogeneity by topographic compartments in muscle-invasive transitional cell carcinoma of the urinary bladder

Superficial transitional cell carcinomas (TCC) of the urinary bladder have been shown to be monoclonal. However, no combined study of clonality and tu mor suppressor genes (TSG) is available to date for muscle-invasive TCC. Fo rty-four muscle-invasive TCC of the urinary bladder selected from women wer e included in this study. Tumor cells located above and below the musculari s mucosa zone were systematically microdissected and used for DNA extractio n. Hha-1 digested and undigested samples were used to study the methylation pattern of androgen receptor alleles and undigested samples were used for microsatellite analysis of TSG (TP53, RB1, WT1, and NF1). Both loss of hete rozygosity (LOH) and single nucleotide polymorphism (SNP) analyses were per formed using optimized denaturing gradient gel electrophoresis. The express ion of p53, pRB, and p21(WAF1) was assessed by immunohistochemistry. Approp riate controls were run in every case. All except two TCC showed a monoclon al pattern with the same allele inactivated in both compartments. Microsate llite analysis of TSG revealed the same LOH/SNP pattern in both tumor compa rtments in 30 cases (involving more than 1 TSG locus in 8) and genetic hete rogeneity in 14 cases. From the latter group, 9 cases expressed more geneti c changes in the deep compartment (involving TP53 gene in all cases, WT1 ge ne in 2, and NF1 in 1), whereas in 4 cases the superficial compartment show ed more genetic changes (three involving NF1 and one involving both RB and TP53). No statistical difference in the immunoexpression was detected, alth ough it tended to be higher in the superficial compartment than in the deep compartment. These concordant data in polymorphic DNA regions indicate tha t bladder-muscle-invasive TCC are monoclonal proliferations with homogeneou s tumor cell selection. Heterogeneous tumor cell selection by topography de fined two different genetic compartments: superficial, NF1-defective, and d eep, TP53-defective. No differences in the immunohistochemical expression w ere observed, precluding a more extensive clinical application.