Evaluation of intensity and pattern of immunohistochemistry staining of CK20 and CK5/6 in high- and low-grade urothelial carcinoma

Introduction: Cytokeratins are specific filaments of epithelial cells. Inappropriate expression of CK5/6 and CK20 has been observed in carcinomas. Objectives: The aim of this study was to compare the immunohistochemical staining pattern and intensity of CK20 and CK5/6 in bladder urothelial carcinoma samples. Materials and Methods: In this cross-sectional study, 60 biopsy and cystectomy samples of papillary urothelial carcinoma patients (including 30 low-grade and 30 high-grade samples) who were admitted to Isfahan Khorshid educational hospital during 2019–2023 were selected using a simple random method. The samples were analyzed and compared according to the intensity and staining pattern of CK20 and CK5/6, as well as the tumor grade. Results: The predominant staining pattern of CK20 in low-grade tumors was the superficial pattern (70.0%), while in high-grade tumors, it was the diffuse or full-thickness pattern (53.3%) (P < 0.001). The most prevalent staining pattern of CK5/6 in low-grade tumors was limited to basal cells (83.3%), whereas no staining was observed in high-grade tumors (56.7%; P < 0.001). Immunoreactivity intensity for CK20 in low- and high-grade tumors was predominantly strong (46.7% and 60.0%, respectively; Mann-Whitney U = 350.5, P = 0.108). In contrast, CK5/6 intensity differed significantly between groups, being predominantly strong in low-grade tumors (80.0%) but predominantly negative in high-grade tumors (56.7%) (Mann-Whitney U = 788.0, P < 0.001). Conclusion: The staining patterns of CK20 and CK5/6 differed between low- and high-grade papillary urothelial carcinomas. Based on this observation, CK20 and CK5/6 may serve as auxiliary markers in conjunction with morphology in the diagnosis and grading of urothelial carcinoma; prospective studies with outcome data are needed to assess any prognostic value.