Comparison of the WHO/ISUP classification and cytokeratin 20 expression inpredicting the behavior of low-grade papillary urothelial tumors

It has not been possible to identify those low-grade papillary transitional cell. bladder tumors that will recur based on conventional histopathologic assessment. Both the new World Health Organization/ International Society of Urologic Pathology (WHO/ ISUP) classification. of transitional cell papi llary neoplasms and the pattern of tumor cytokeratin 20 (CK20) immunostaini ng have been suggested as means of improving prognostication in low-grade t ransitional cell tumors. Forty-nine low-grade, noninvasive papillary transi tional cell tumors were identified for the period between 1984 and 1993, Th e recently described WHO/ISUP classification was applied, and the tumors we re classified histologically as papilloma, papillary neoplasm of low malign ant potential (LMP) or low-grade papillary carcinoma After CK20 immunostain ing, the expression pattern in the tumor was classified as normal (superfic ial) or abnormal. Of 49 tumors, 20 were classified as papillary neoplasms o f LMP and five of these patients (25%) experienced a recurrence. Of 29 tumo rs classified as low-grade papillary carcinoma, 14 (48.2%) recurred, In 46 of 49 cases, the CI(20 immunostaining could be evaluated. Sixteen tumors sh owed normal (superficial) pattern of CK20 expression, and four (25%) of the se patients experienced a recurrence. In contrast, of 30 patients with abno rmal CK20 staining of their tumors, 15 (50%) patients had one or more recur rences, In this study papillary neoplasms of LMP (as per the WHO/ ISUP clas sification system) had a lower recurrence rate than low-grade papillary tra nsitional cell carcinoma Similarly low-grade urothelial tumors showing a no rmal CK20 expression pattern recurred less frequently than tumors with an a bnormal pattern of CK20 staining. Neither of these differences was statisti cally significant, and recurrences were observed in 20% of patients whose t umors were both classified as papillary neoplasms of LMP and showed normal CK20 immunostaining; thus they do not allow a change in our current managem ent of patients with low-grade papillary urothelial tumors, with dose follo w-up for all patients.