Histomorphology and expression immunohistochemistry of CK20 in bladder urothelial carcinoma histopathology subtypes

Background: Bladder urothelial carcinoma is one of the most common malignancies of the urinary tract, with varying histopathological subtypes that influence prognosis and treatment strategies. Identifying the histomorphology and immunohistochemistry (IHC) expression patterns of cytokeratin 20 (CK20), a marker frequently used in urothelial carcinoma diagnosis, can aid in understanding the tumor’s biological behavior and its histopathological classification. This study aims to evaluate the histomorphology and CK20 expression across histopathology subtypes of bladder urothelial carcinoma. Methods: This descriptive study was conducted at the Anatomical Pathology Installation of Prof. Dr. Chairuddin P. Lubis Universitas Sumatera Utara Hospital. A total of 77 paraffin-embedded tissue blocks from transurethral bladder tumor resections were included. Subtypes were confirmed based on the 2022 WHO Classification of Tumors (Urinary and Male Genital Systems). CK20 expression was assessed using IHC, with scores categorized as low (scores 1–2) or high (scores 3–4). Results: The study comprised 77 urothelial carcinoma cases: 66 male (84.6%) and 11 female (15.4%), with ages ranging from 50 to 70 years. Clear cell (glycogen-rich) urothelial carcinoma was the most common subtype (19 cases, 24.7%). Lymphovascular invasion was observed in 18 cases (23.4%), with no evidence of perineural invasion. CK20 IHC expression was negative in 51 cases (66.2%), weak in 22 cases (26.6%), and strong in 4 cases (5.2%). Conclusion: Clear cell (glycogen-rich) urothelial carcinoma is the predominant histopathology subtype of bladder urothelial carcinoma. Most cases showed negative CK20 IHC expression, underscoring the variability in marker expression across subtypes. These findings support the role of histomorphological and IHC evaluation in guiding bladder urothelial carcinoma diagnosis and management.