Noninvasive Papillary Basal-like Urothelial Carcinoma: A Subgroup of Urothelial Carcinomas With Immunohistochemical Features of Basal Urothelial Cells Associated With a High Rate of Recurrence and Progression

Background:We investigated the clinical and pathologic significance of a subgroup of noninvasive papillary urothelial carcinomas (UCs) expressing reactivity to urothelial basal cell markers.Design:In total, 302 consecutive cases of noninvasive papillary UC were evaluated immunohistochemically with cytokeratin 5 (CK5)/CD44. Any UC that was reactive for greater than 25% thickness of the urothelium was designated as basal-like urothelial carcinoma (BUC); remaining UC cases were designated as non-BUC. The follow-up period was up to 3 years. Historical review of UC was extended for up to 3 retrospective years.Results:Among 302 noninvasive UC, BUC was identified in 33 of 256 (12.9%) low-grade UC and 8 of 46 (17%) high-grade UC (P=0.041). Immunoreactivity for CD44 was similar to that of CK5, but displayed weaker and more diffuse staining. CK20 was reactive in 9 cases, primarily high-grade BUC. Other basal cell markers (34bE12, p63, bcl2, and EP4) were found to be neither sensitive nor specific in detecting UC with high CK5 expression. In comparison with non-BUC, BUC was associated with increased multifocality, larger tumor size, higher recurrence rate, and more frequent upgrading and stage progression. In the follow-up period of 3 years, distant metastasis occurred in 6 cases of which 5 were in the BUC subgroup.Conclusions:Our results showed that noninvasive papillary BUC represents a small subset associated with increased risk of tumor recurrence and progression. The aggressive behavior is likely associated with basal-like features of BUC, as seen in carcinomas with basal cell features in other body sites.