Comprehensive analyses of PBRM1 in multiple cancer types and its association with clinical response to immunotherapy and immune infiltrates

Background

The prognostic value of polybromo 1 (PBRM1) gene mutations in clear cell renal carcinoma (CCRCC) with anti-programmed death-ligand 1 (PD-L1) therapy remains controversial, and few studies have reported the impact of PBRM1 mutations in other cancer types.

Methods

The patient information was obtained from cBioPortal and the Tumor Immune Estimation Resource (TIMER) databases. Mann-Whitney U test were used for correlation analysis. For survival analyses, Kaplan-Meier survival curves were used and compared using the log-rank test. Cox’s regression model was used to perform univariable and multivariable analyses

Results

Our study, for the first time, performed comprehensive analyses of PBRM1 mutation frequency, PBRM1 expression, relationship of PBRM1 mutations with clinical benefit from immunotherapy, and PBRM1 expression with immune infiltrates in diverse cancer types. The results showed that the expression of PBRM1 was significantly lower in diverse cancer types compared with normal tissues. Based on multivariable analysis, PBRM1 mutations trended towards worse clinical outcomes from anti-PD-L1 in CCRCC, lung adenocarcinoma (LUAD), bladder urothelial carcinoma (BLCA), and skin cutaneous melanoma (SKCM), and a significant association was observed in LUAD and BLCA. PBRM1 mutations were associated with higher TMB in diverse cancer types and significant associations were observed in LUAD and BLCA. The expression of PBRM1 was found to positively correlate with immune infiltrates in diverse cancer types.

Conclusions

Our findings suggested caution in starting immunotherapy alone in PBRM1 mutant patients. Further studies are needed to improve treatment for PBRM1 mutant patients.

Mutational Analysis of PBRM1 and Significance of PBRM1 Mutation in Anti-PD-1 Immunotherapy of Clear Cell Renal Cell Carcinoma

Renal cell carcinoma is a common solid tumor. PBRM1 is one of the most mutation-prone genes in clear cell renal cell carcinoma (ccRCC) with the occurrence of mutation in 40% of ccRCC patients. Mutations in PBRM1 have been correlated with the efficacy of immunotherapy. However, the mutation types of PBRM1 are not well characterized. The effects of PBRM1 expression levels in the tumor microenvironment are not well studied. In addition, the mechanism and effect of anti-PD-1 immunotherapy in ccRCC tumor microenvironments are not well clarified. In this study, using bioinformatics methods we analyzed the alternation frequency and expression levels of PBRM1 in various tumors. Next, we experimentally validated their expression levels in ccRCC tissues from human and mouse models. We attempted to clarify the mechanisms of anti-PD-1 immunotherapy in ccRCC with various PBRM1 expression levels. Our results showed that deficiency of PBRM1 protein is correlated with CD4 T cell reduction in human and mouse ccRCC tissues. We also showed that anti-PD-1 Immunotherapy can increase the infiltration of T cells in both PBRM1 high and PBRM1 low tumors but to different degrees. Our study indicates that the reduction of CD4 cells in tumor tissues with low expression of PBRM1 may explain the compromised efficacy of anti-PD-1 immunotherapy in patients with PBRM1 mutated ccRCC. Our study sheds light on the potential of PBRM1 as a therapeutic target in ccRCC.