Cytokeratin 20 as an objective marker of urothelial dysplasia.

To investigate the dysregulation of cytokeratin 20 (CK20) expression in urothelial dysplasia and its potential as a diagnostic aid. Twenty-two patients were selected on the basis that they had undergone one or more biopsies showing dysplasia before the development of a transitional cell carcinoma (TCC): 15 of these patients also had a prior history of TCC. The dysplasia was classified as mild in 12, moderate in 14 or severe dysplasia/carcinoma in situ in 10 patients, ensuring that a spectrum of morphological appearances was represented. Control biopsies were obtained from seven children undergoing bladder reconstructions and 23 patients with recurrent urinary tract infections, haematuria or functional bladder symptoms, but no history of TCC. The expression of CK20 was restricted to superficial 'umbrella' cells and occasional intermediate cells in the control biopsies, even in the presence of severe inflammation. In 31 of the 36 cases of dysplasia complete loss of restriction was seen at least focally with positive expression in all layers of the urothelium. The abnormal expression of CK20 is a reliable, positive marker of urothelial dysplasia in the urinary bladder. Immunostaining for CK20 is therefore a useful adjunct to morphology in the diagnosis of dysplasia, of particular value in the distinction from reactive states where diagnostic difficulties are greatest.