Abstract 6479: High expression of the exhaustion markers PD-1 and PD-L1 in non-muscle invasive bladder cancer is associated with poor outcome following Bacillus Calmette-Guérin immunotherapy

Abstract Introduction: The recommended treatment for high-risk non-muscle invasive bladder cancer (NMIBC) includes intravesical instillations of Bacillus Calmette-Guérin (BCG). Despite completing BCG therapy, up to 40 % of patients experience disease recurrence within five years. T cell exhaustion has been associated with poor outcome following treatment with BCG. In this study, we investigated whether T cell exhaustion, characterized by protein expression of PD-1 and PD-L1 in paired samples obtained before and after BCG treatment could provide further insight into BCG response and help predict outcome in patients with NMIBC. Methods: We included 105 patients with NMIBC, with transurethral resection of bladder tumor (TURBT) samples obtained prior to BCG (n=122) and after in cases with disease recurrence (n=44). Tissue sections from tissue microarrays (TMAs) were stained using immunohistochemistry to analyze the protein expression of the exhaustion markers PD-1 (clone EP239) and PD-L1 (clone 22C3). Data was analyzed using digital pathology software. Cells were scored as positive when detection of a nucleus was combined with a positive PD-1 or PD-L1 stain in both tumor or stromal area (defined by presence of positive pan-CK stain or not, respectively). In total, 167 samples were considered suitable for further analysis (cell count > 200 in tumor and stromal areas). Stratification of samples into high or low expression was based on a median split of the positive cell fraction. Results: When investigating the fraction of PD-1 and PD-L1 positive cells in the tumors, we observed that PD-1 expression significantly increased with tumor stage in pre- (p=0.002) and post-BCG (p=0.006) tumor samples. PD-1 expression was also increased in high-grade tumors compared to low-grade tumors in pre-BCG samples (p = 0.001). Furthermore, we observed a significant association between tumors of higher stage and high PD-L1 expression in the pre-BCG samples (p = 0.007). Patients with low expression of PD-1 and PD-L1 in the pre-BCG tumor samples had a superior high-grade recurrence-free survival (HG-RFS) compared to patients with high PD-1 (p=0.002) and PD-L1 (p=0.021) expression. In addition, low expression of PD-L1 in pre-BCG tumors was correlated with a better progression-free survival compared to the patients with high PD-L1 expression (p = 0.013). When creating a combined score with PD-1 high and PD-L1 high samples, we saw that these patients demonstrated a worse HG-RFS compared to patients with either mixed or low scores (p = 0.005). Conclusion: Protein expression of the exhaustion markers PD-1 and PD-L1 in pre-BCG tumor samples were correlated to higher stage and grade as well as worse HGFRS, indicating that T cell exhaustion plays an important role in resistance to BCG treatment and may be used to guide treatment. Citation Format: Tine G. Andreasen, Trine Strandgaard, Line Raaby, Jørgen Bjerggaard Jensen, Lars Dyrskjøt. High expression of the exhaustion markers PD-1 and PD-L1 in non-muscle invasive bladder cancer is associated with poor outcome following Bacillus Calmette-Guérin immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6479.