Evaluation of BRCA1 and BRCA2 as Indicators of Response to Immune Checkpoint Inhibitors

Immune checkpoint inhibitors (ICIs) have achieved impressive success in a subset of malignant tumors. Tumor mutation burden (TMB), programmed cell death ligand 1 expression, and deficient DNA mismatch repair are the few biomarkers known to be associated with response to ICIs. Breast cancer type 1 or 2 susceptibility gene (BRCA1 [OMIM 113705] and BRCA2 [OMIM 600185]) play critical roles in DNA repair. However, the roles of BRCA1/2 alteration in tumor immunotherapy remains uncharacterized, to our knowledge. Several early phase clinical trials are examining the combination of ICIs and poly(ADP-ribose) polymerase inhibitor in BRCA1/2 altered tumors. The role of BRCA1/2 alteration in immunotherapy remains controversial across different tumor types. We hypothesized that BRCA1/2 alteration is associated with TMB and may serve as a novel indicator associated with better treatment outcomes of ICIs.