Cytokeratin 20 expression is linked to stage progression and to poor prognosis in advanced (pT4) urothelial carcinoma of the bladder

Cytokeratin 20 (CK20) expression is limited to umbrella cells in the normal urothelium. Since CK20 is often upregulated in neoplastic urothelial cells including dysplasia and carcinoma in situ, immunohistochemical CK20 analysis is often used for the assessment of bladder biopsies. CK20 expression is a feature of luminal bladder cancer subtype, but its prognostic relevance is disputed. In this study, we investigated CK20 on >2700 urothelial bladder carcinomas in a tissue microarray format by immunohistochemistry. Cytoplasmic and membranous CK20 staining was seen in 1319 (51.8%) cancers. The fraction of CK20 positive and especially strongly positive cases increased from pTaG2 low grade (44.5% strongly positive) and pTaG2 high grade (57.7%) to pTaG3 high grade (62.3%; p = 0.0006) but was lower in muscle-invasive (pT2–4) carcinomas (51.1% in all pTa vs. 29.6% in pT2–4; p