Comparative evaluation of PD-L1 expression and tumor immune microenvironment in molecular subtypes of muscle-invasive bladder cancer and its correlation with survival outcomes.

Objectives: Immune checkpoint inhibitors have revolutionized treatment of platinum-refractory advanced bladder cancer, offering hope where options are limited. Response varies, however, influenced by factors such as the tumor's immune microenvironment and prior therapy. Muscle-invasive bladder cancer (MIBC) is stratified into molecular subtypes, with distinct clinicopathologic features affecting prognosis and treatment. This study assessed the expression of programmed cell death 1 ligand 1 (PD-L1) and other immune markers in MIBC, categorized by molecular phenotype.

Methods: Using GATA3 and CK5/6 immunohistochemistry, 90 neoadjuvant chemotherapy-naive MIBC cases were classified into luminal and non-luminal subtypes. The immune microenvironment was characterized through immunostaining for PD-L1, CD4, and CD8. We applied PD-L1 positivity thresholds of 1% or greater for tumor cells and 5% or greater for immune cells. Tumors were examined for PD-L1 expression, histologic subtypes, and immune cell infiltration.

Results: Varied expression of PD-L1 and T-cell subtype densities were observed among MIBC subtypes. The double-negative subtype displayed the highest PD-L1 immune cell expression and stromal CD4 and CD8 T-cell densities, indicating an active immune profile. The basal subtype exhibited the highest PD-L1 positivity in tumor cells. In contrast, the luminal type showed the lowest PD-L1 tumor and immune cell expression, with high intratumoral CD4 T-cell density. Although PD-L1 expression in tumor or immune cells did not independently affect survival, patients with basal and double-negative tumors had poorer overall survival.

Conclusions: This study highlighted the immune diversity of MIBC in the context of molecular subtypes. Distinct molecular and immune profiles could guide the development of predictive signatures for enhanced immunotherapy response in advanced bladder cancer.