Nested and microcystic variants of urothelial carcinoma displaying immunohistochemical features of basal‐like urothelial cells: An immunohistochemical and histopathogenetic study

Abstract

Nested/microcystic ( NV / MV ) urothelial carcinoma ( UC ) variants are associated with mild cytologic atypia and commonly present at high‐stage disease. The histopathogenesis is investigated using urothelial basal cell markers. Archival 14 NV / MV and three inverted papilloma ( IP ) were immunostained for CD44 , cytokeratin 5 ( CK5 ), CK34bE12 and p63. Twenty consecutive cases of invasive high‐grade UC including 14 superficial and 6 muscle‐invasive UC cases were used as control. Immunostaining was scored as high for staining of full or more than 50% thickness of the epithelial nest or epithelium and low for lesser immunoreactivity and negative reactivity. All 14 NV / MV , 3 IP and 6 control cases showed a high score of immunoreactivity for CK5 , CD44 , CK34bE12 and focally for p63. The remaining control cases showed a high score of immunoreactivity for CK34bE12 , while negative or low for CK5 , CD44 and p63. In conclusion, immunoreactivity CK5 and CD44 commonly immunostained NV / MV and some invasive high grade UC . Other basal cell markers ( CK34bE12 and p63) appear to be non specific or non sensitive. NV and MV and some UC likely represent a subset of UC displaying immunohistochemical features of urothelial basal cells. They had tendency of endophytic growth and early invasion despite the innocuous cytologic appearance.