Evaluation of PD-L1 expression in PBRM1-altered clear cell renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) often harbors Polybromo 1 (PBRM1) alterations. These alterations are associated with immune checkpoint blockade response in ccRCC, particularly antiprogrammed cell death 1 (PD1)/programmed cell death ligand 1 (PD-L1)-targeted therapy. However, the association between PBRM1 alterations and PD-L1 expression in ccRCC remains unclear.

We analyzed alterations in PBRM1 and PD-L1 expression using immunohistochemistry (IHC) targeting PBRM1 and PD-L1 (22C3) in tissues collected from patients with localized ccRCC (Cohort 1) and advanced ccRCC (Cohort 2). Additionally, next-generation sequencing (NGS) was conducted on Cohort 2 patients to analyze PBRM1 alterations.

Cohort 1 comprised 526 patients, of whom 139 (26.4%) exhibited PD-L1 positivity and 205 (38.9%) exhibited loss of PBRM1 expression in IHC. PD-L1 expression was positively associated with the loss of PBRM1 expression (P < 0.001) in localized ccRCC. Kaplan-Meier analysis indicated that PBRM1 expression loss and PD-L1 expression positively correlated with tumor recurrence (P < 0.001 and P = 0.003, respectively). Cohort 2 comprised 59 patients with advanced ccRCC, of whom 33 (56.9%) exhibited PBRM1 genetic alterations. PBRM1 IHC exhibited a sensitivity of 84.48% and specificity of 87.5% compared to NGS results. We did not find a significant association between PBRM1 mutation and PD-L1 expression, in contrast to the findings in Cohort 1. However, we frequently observed that PBRM1 mutation and PD-L1 expression occur concurrently, with 60% of PBRM1-altered ccRCC cases being PD-L1 positive.

Although our study did not establish a correlation between PBRM1 mutations and PD-L1 expression, it demonstrated that the occurrence of PBRM1-altered ccRCC with PD-L1 expression is not uncommon. Therefore, the presence of PBRM1 alterations may challenge the use of PD-L1 IHC as a predictive marker for PD-L1 blockade in ccRCC.