Tertiary lymphoid structures in urothelial carcinoma: bridging spatial architecture with therapeutic vulnerability in the post-BCG era.

Urothelial carcinoma (UC) remains a persistent clinical challenge in the post-Bacillus Calmette-Guérin (BCG) era, particularly because a substantial proportion of patients with high-risk non-muscle-invasive bladder cancer (NMIBC) experience recurrence or progression despite standard intravesical immunotherapy. Although immune checkpoint inhibitors (ICIs) and antibody-drug conjugates (ADCs) have expanded the therapeutic armamentarium, widely studied biomarkers such as tumor mutational burden (TMB) and PD-L1 expression show limited and inconsistent predictive performance in UC, which may partly reflect their inability to capture the spatial organization and functional states of the tumor immune microenvironment (TIME). Tertiary lymphoid structures (TLS), ectopic lymphoid aggregates that develop in non-lymphoid tissues at sites of chronic inflammation or cancer, have emerged as candidate mediators and spatial markers of local adaptive immunity. In UC, TLS appear to exhibit spatial heterogeneity and may exist across a maturation continuum from early, disorganized lymphoid aggregates to mature, germinal center-containing follicles; their localization within the lamina propria, tumor stroma, or invasive front may be associated with distinct immune contexts and clinical outcomes. This review provides a urology-centric perspective on TLS biology in UC, emphasizing how the anatomical and immunological niche of the bladder, including urinary exposure, the urinary microbiome, BCG-associated inflammation, and stromal remodeling, may shape the conditions under which TLS develop and function. We critically discuss TLS maturation status as a potential spatial biomarker, while emphasizing that its relationship with BCG failure and subsequent response to PD-1/PD-L1 blockade or enfortumab vedotin (EV)-based therapy remains largely correlative and requires prospective validation. Furthermore, we explore emerging strategies that may modulate TLS-associated immune architecture, including STING agonist instillation and LTβR pathway modulation, and discuss how TLS could be tested as an adjunctive biomarker in future bladder-preservation studies for high-risk T1 disease. By synthesizing current evidence and methodological advances in spatial transcriptomics, we underscore the translational imperative of viewing UC as a malignancy with heterogeneous local immune architecture, including candidate tertiary lymphoid structures. At present, TLS should not be used as a stand-alone biomarker for selecting bladder preservation, radical cystectomy, intravesical therapy continuation, or systemic treatment switching.