Objective: In order to improve the diagnostic accuracy of urothelial tumors, a technology of molecular cytogenetic analysis was applied to bladder washings. Study design: Multicolor - FISH (fluorescence in situ hybridization, UroVysion® ) was applied to specimens prepared by the liquid-based cytology (LBC) method for 305 bladder washings. FISH data was compared with cytological findings. Results: The cytological examination classified tumors into three categories; negative, equivocal, and malignant for 34.1%, 30.2%, and 35.7% of 305 specimens, respectively. UroVysion using three centromere probes for chromosomes 3, 7, and 17, and a locus specific probe for 9p21 harboring p16INK4a allowed diagnosis as follows. When more than 10% of epithelial cells show numerical aberrations of signal spots at least in one of 3 CEPs or when more than 7% of epithelial cells have less than 2 spots of 9p21, the tumor is classified as urothelial carcinoma. Furthermore, the tumor in which the 'variant fraction size' of CEPs is less than 15% is categorized as low-grade carcinoma. The tumor in which the 'variant fraction size' of CEPs is more than 15% is categorized as high-grade carcinoma. Negative, low-grade carcinoma, and high-grade carcinoma accounted for 35.4%, 27.5%, and 37.1% of 305 cases, respectively. In this series, 69.5% of cytogenetically negative tumors were cytologically diagnosed as negative, and 80.5% of high-grade carcinomas were cytologically diagnosed as positive. Conclusion: The multicolor-FISH analysis allows a diagnosis of urothelial tumors.
