Impaired DNA repair drives mutagenicity, which increases neoantigen load and immunogenicity. We investigated the expression of proteins involved in the DNA damage response (ATM, Chk2), double-strand break repair (BRCA1, BLM, WRN, RECQL4, RECQL5, TOPO2A, DNA-PKcs, Ku70/Ku80), nucleotide excision repair (ERCC1), base excision repair (XRCC1, pol β, FEN1, PARP1), and immune responses (CD8, PD-1, PD-L1, FOXP3) in 1269 breast cancers and validated our findings in an independent estrogen receptor (ER)- cohort (n = 279). Patients with tumors that expressed low XRCC1, low ATM, and low BRCA1 were not only associated with high numbers of CD8+ tumor-infiltrating lymphocyte (TILs), but were also linked to higher grades, high proliferation indexes, presence of dedifferentiated cells, ER- cells and poor survival (all P ≤ 0.01). PD-1+ or PD-L1+ breast cancers with low XRCC1 were also linked to an aggressive phenotype that was high grade, had high proliferation indexes, contained dedifferentiated cells and ER- (all with P values ≤ 0.01) and poor survival (P = 0.00021 and P = 0.00022, for PD-1+ and PD-L1+ cancers, respectively) including in an independent ER- validation cohort (P = 0.007 and P = 0.047, respectively). We conclude that the interplay between DNA repair, CD8, PD-L1, and PD-1 can promote aggressive tumor phenotypes. XRCC1-directed personalization of immune checkpoint inhibitor therapy may be feasible and warrants further investigation in breast cancer.
- Received August 4, 2016.
- Revision received February 2, 2017.
- Accepted February 20, 2017.
- Copyright ©2017, American Association for Cancer Research.