Expression of cytokeratin 20 in urine cytology smears: a potential marker for the detection of urothelial carcinoma

Background: Urine cytomorphology is one of the oldest methods for screening and monitoring patients with transitional cell carcinoma (TCC). Sensitivity of urine cytology is relatively low. Ancillary techniques on urine sample may increase the sensitivity. Aim: To explore the utility of cytokeratin 20 (CK20) immunostaining in identifying malignant cells in urine cytology smears. Materials and methods: Fourteen cases each of confirmed TCC and benign urinary cytology along with five cases of atypical cells in urine were immunostained with a monoclonal CK20 antibody. Of 14 cases of TCC, 12 showed strong positive staining with the antibody. All benign cases were negative except for a few cases in which the umbrella cells were weakly to moderately positive. In all five cases of atypical urine cytology the atypical cells stained positive with the antibody. These cases were later confirmed as TCC on histopathology of bladder wall biopsy. Conclusion: CK20 is an important biomarker that can be used to identify TCC in urine cytology smears. It is particularly useful in those cases where malignancy cannot be confirmed by morphology alone.