Impact of Photodynamic Diagnosis on Immune Cell Infiltration in BCG-treated Non–muscle-invasive Bladder Cancer

Background and objective Photodynamic diagnosis (PDD) is used during transurethral resection of bladder tumors (TURBT) to improve detection of non–muscle-invasive bladder cancer (NMIBC). Emerging evidence suggests that PDD may also influence immune activation. We investigated whether PDD is associated with immune-related changes in tumors and urine from patients with NMIBC receiving Bacillus Calmette-Guérin (BCG) immunotherapy. Methods We retrospectively analyzed paired pre- and post-BCG samples from 156 patients with NMIBC with detailed clinical data. PDD exposure was determined from medical records and defined as PDD use within 100 days before BCG induction. PDD status was linked to existing multi-omics data, including urine proteomics (Olink), tumor ribonucleic acid (RNA) sequencing, and imaging mass cytometry (IMC) for spatial immune profiling. Findings and limitations Urine proteomics showed post-BCG upregulation of immune-related proteins, including programmed death-1 and vascular endothelial growth factor receptor-2, in PDD-exposed patients. In contrast, RNA sequencing suggested increased post-BCG infiltration of multiple immune cell populations (B cells, T cells, cytotoxic cells, and mast cells) in No PDD patients but not in PDD-exposed patients. Consistently, IMC indicated increased infiltration of cluster of differentiation (CD)4⁺, CD8⁺, and natural killer cells post-BCG in No PDD exposed patients, with minimal changes in PDD-exposed patients. The exploratory design and potential confounding limit causal interpretation, and no clear association with clinical outcomes was demonstrated. Conclusions and clinical implications This exploratory and biologically focused study suggests that while PDD appears to modulate the local urinary proteome, no clear shifts in tumor immune cell infiltration were observed. These findings do not support a consistent effect of PDD on the tumor immune microenvironment, and no association with clinical outcomes was observed. Determining whether the added benefit of PDD stems purely from enhanced diagnostics or includes a direct immunomodulatory effect warrants further investigation.