The biological behaviors of urothelial carcinomas are linked roughly to histological grade, but there are many cases whose precise classification is difficult. In addition, it remains unclear whether there are differences in the types of genetic changes between low- and high-grade urothelial carcinomas. Fifty-seven biopsy specimens of urothelial carcinomas and 9 control urothelial specimens were examined by four-color FISH with centromere-specific probes for chromosomes 3, 7, and 17, and a locus-specific probe for 9p21 that covers p16INK4a and p15INK4b. Nuclear DNA ploidy was determined with laser scanning cytometry (LSC). FISH and LSC data allowed us to classify urothelial cancers into two groups. Tumors in one group showed minimal intercellular variation in centromere copy numbers and DNA diploidy, and these tumors were histologically comparable to low-grade (grades I and II) tumors. In contrast, tumors in the other group showed a large intercellular variation in centromere copy numbers and DNA aneuploidy, suggesting chromosomal instability. These tumors were all high-grade (grades II and III) tumors. Numerical abnormalities of 9p21 signals were detected in all cancers; this variation in 9p21 signals was also associated with histological grade. The present findings suggest that the pathogenetic pathways are different between low- and high-grade carcinomas. High-grade tumors are characterized by chromosomal instability, whereas low-grade carcinomas are not.

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