TROP-2 and Nectin-4 Expression in Muscle-Invasive Urothelial and Rare Non-Urothelial Bladder Carcinoma: Association with Tumour Stage and Clinical Outcome.

Background/Objectives: Antibody-drug conjugates (ADCs) targeting Nectin-4 (enfortumab vedotin) and TROP-2 (sacituzumab govitecan) have transformed the management of advanced urothelial carcinoma (UC), but evidence on their molecular targets in rare non-urothelial bladder carcinomas (N-UC) is scarce. We evaluated the immunohistochemical expression of TROP-2 and Nectin-4 in muscle-invasive UC and N-UC and assessed their association with tumour stage, nodal status and overall survival. Methods: In this retrospective single-centre study, 111 consecutive patients with primary muscle-invasive bladder carcinoma (73 UC, 38 N-UC including squamous, adenocarcinoma, neuroendocrine and sarcomatoid variants) were analysed. TROP-2 and Nectin-4 expression was quantified using the H-score; positivity was defined as ≥15. Marker expression was correlated with clinicopathological characteristics and overall survival (OS) using chi-squared, linear-by-linear, log-rank, and Cox regression analyses. Results: TROP-2 positivity was observed in 46.6% of UC and 36.8% of N-UC (p = 0.925); Nectin-4 positivity in 17.8% and 28.9%, respectively (p = 0.275). Among positive cases, TROP-2 H-scores were higher in N-UC than in UC (mean 109 vs. 70; Mann-Whitney p = 0.045; Cliff's delta 0.37, 95% CI 0.05-0.66); as no adjustment for multiple testing was applied, this difference is regarded as nominally significant and exploratory. Nectin-4 H-scores were numerically higher in UC (mean 82 vs. 53) but did not reach statistical significance (p = 0.84). Across the cohort, TROP-2 expression increased with advancing T stage (linear-by-linear p = 0.026) and was associated with nodal involvement (p = 0.043). Nectin-4 showed no significant stage association. Sarcomatoid carcinomas were negative for both markers. Median OS was 41 months in UC versus 19 months in N-UC (p = 0.668). Neither marker independently predicted OS, whereas advanced T stage (p = 0.003) and nodal involvement (p = 0.021) were significantly associated with poorer survival; T stage remained independently prognostic in multivariable analysis. Conclusions: TROP-2 and Nectin-4 are expressed at comparable rates in muscle-invasive UC and rare N-UC, except in sarcomatoid variants. TROP-2 expression increased with advancing tumour stage, suggesting stage-dependent regulation in muscle-invasive disease. Therefore, both markers should be interpreted as potential therapeutic targets whose expression can be demonstrated in these tumours, rather than as prognostic biomarkers or as validated predictive biomarkers of ADC response; because no patient received an ADC, the present study cannot determine whether expression predicts clinical benefit, and this distinction requires prospective, treatment-linked evaluation that includes patients with N-UC.