Basal subtype of invasive urothelial carcinoma of the bladder has aggressive behavior and poor prognosis: An immunohistochemistry-based study.

Introduction: Molecular subtyping of urothelial cancer of the bladder can help in identifying aggressive subtypes and aid in the prognostication of the disease. These subtypes can be broadly identified with the help of immunohistochemistry (IHC) markers reliably.

Aims: To assess the molecular subtypes of urothelial carcinoma of the bladder using IHC markers and evaluate their association with clinicopathological characteristics and overall survival (OS).

Materials And Methods: This was a cross-sectional study done over 3 years in a tertiary care center. There were 109 cases of invasive urothelial carcinoma of the bladder. In 43 cases, radical cystectomy was performed, and 66 cases underwent transurethral resection of bladder tumor. CK5/6, and CK14 were used as markers of the basal subtype; GATA-3 and CK20 were used for the luminal subtype. Cases were classified into basal, luminal, double-positive, and double-negative subtypes. The association of molecular subtypes with clinicopathological characteristics was analyzed. OS was analyzed for the molecular subtypes. All the relevant statistical tests were performed using IBM SPSS software version 24.0.

Results: The most frequently occurring molecular subtype was luminal (GATA3+, CK5/6-) in 62% of cases. Tumors with the basal subtype showed a higher frequency of muscle invasion compared to nonbasal types and presented as high-grade tumors. The luminal subtype was significantly associated with conventional histology and lamina propria invasive tumors. The basal molecular subtype showed a mean OS of 15 (±4) months, which was significantly worse than that of nonbasal subtypes.

Conclusion: The basal subtype of urothelial carcinoma of the bladder behaves more aggressively in terms of grade, extent of invasion, and OS.