PD-L1 expression in high-risk non-muscle invasive bladder cancer is not a biomarker of response to BCG.

Purpose: Up to 50% of high-risk non-muscle invasive bladder cancer (HR-NMIBC) patients fail Bacillus Calmette-Guérin (BCG) treatment, resulting in a high risk of progression and poor clinical outcomes. Biomarkers that predict outcomes after BCG are lacking. The antitumor effects of BCG are driven by a cytotoxic T cell response, which may be controlled by immune checkpoint proteins like Programmed Death Ligand 1 (PD-L1). Here, we hypothesized that PD-L1 protein expression could serve as a biomarker for BCG-failure.

Methods: HR-NMIBC patients who received ≥ 5 BCG instillations were included. Tissue microarrays were constructed from BCG-naïve tumors and recurrences and stained with the PD-L1 (SP142) antibody. PD-L1 status was defined as ≥ 5% tumor-infiltrating immune cells with membrane staining in the tumor area. Clinicopathological associations with PD-L1 positive tumors were investigated, and time-to-event analyses were performed comparing PD-L1 positive vs. negative tumors.

Results: 432 BCG-naïve tumors and 160 recurrences were included, and 91% of patients received adequate BCG. In BCG-naïve tumors, PD-L1 was expressed in 7% of patients and PD-L1 expression was associated with stage T1 versus Ta disease (p = 0.015). PD-L1 expression was not associated with treatment failure after adequate BCG (p = 0.782) nor with progression-free survival (p = 0.732). Testing cut-offs of ≥ 1% and ≥ 10% PD-L1 positivity did not alter results. High PD-L1 expression was more frequent in tumor recurrences (14%) as compared to BCG-naïve tumors (p = 0.012).

Conclusion: PD-L1 expression in HR-NMIBC is not a biomarker of response to BCG. However, PD-L1 is higher in a subset of tumors that failed BCG treatment. More research is needed to determine the role of PD-L1 in tumors where BCG treatment failed.