KRT20 and cancer: Another valuable study reported that all cases (100%) of normal urothelia had normal expression patterns with Cytokeratin 20 and ninety-six percent of morphologically unequivocal cases of reactive urothelial atypia (RUA) showed normal expression patterns of Cytokeratin 20 whereas, in the carcinoma in situ (CIS) group, 86% had abnormal CK20 expression [7].