Immunohistochemical evaluation demonstrates retained apical and membranous uroplakin expression within the umbrella-cell layer. CK and CK5/6 show diffuse staining throughout the urothelial thickness. CK20 staining is confined to the umbrella cells. The Ki-67 (MIB-1) proliferation index is moderately increased, with scattered nuclear labeling involving approximately 15% of the lesional cells. p53 exhibits a wild-type staining pattern, characterized by focal weak nuclear reactivity.
Urinary bladder mass.
One referred paraffin block and two H&E stained slides coded S5533-2025.
Referred slides and block of urinary bladder mass TUR and immunostaining:
COMMENT:
The presence of diffuse CK5/6 expression accompanied by a moderately elevated proliferative index suggests disturbed urothelial maturation and increased proliferative activity, findings that are atypical for a conventional urothelial papilloma. Accordingly, the diagnostic considerations extend to low-grade papillary urothelial carcinoma.