Histologic grading of noninvasive papillary urothelial tumors: validation of the 1998 WHO/ISUP system by immunophenotyping and follow-up.

Cytokeratin (CK) 20, Ki-67, and p53 were applied to 84 noninvasive papillary urothelial tumors graded by the 1973 World Health Organization (WHO) and 1998 WHO/International Society of Urological Pathology (ISUP) systems. In the WHO/ISUP classification, all benign lesions showed normal CK20 staining and all carcinomas showed abnormal staining. The Ki-67 index was significantly different between benign and malignant lesions (P < .05) and between low- and high-grade carcinomas (P < .001). p53 was negative in all benign lesions, with a significant difference between low- and high-grade carcinomas (P < .001). Tumor recurrence was significantly different between low- and high-grade carcinomas (no recurrences among the papillary urothelial neoplasms of low malignant potential). By the 1973 WHO classification, normal CK20 staining was present both in benign lesions and in carcinomas. Ki-67 staining did not distinguish between grade 2 and grade 3 carcinomas (P > .05), and there was no difference in p53 staining in grades 1 and 2 carcinomas (P > .05). Recurrences were not different between grades 1, 2, and 3 carcinomas. All biologic markers studied and tumor recurrences were significantly different among papillary lesions classified by the WHO/ISUP system but not by the 1973 WHO system, validating the predictive value of the WHO/ISUP system and providing objective markers for the grading of papillary urothelial tumors.