Jin‐Ku Lee

Homologous recombination deficiency (HRD) is a crucial driver of tumorigenesis by inducing impaired repair of double‐stranded DNA breaks. Although HRD possibly triggers the production of numerous tumor neoantigens that sufficiently stimulate and activate various tumor‐immune responses, a comprehensive understanding of the HRD‐associated tumor microenvironment is elusive. To investigate the effect of HRD on the selective enrichment of transcriptomic signatures, 294 cases from The Cancer Genome Atlas‐Ovarian Cancer project with both RNA‐sequencing and SNP array data are analyzed. Differentially expressed gene analysis and network analysis are performed to identify HRD‐specific signatures. Gene‐sets associated with mitochondrial activation, including enhanced oxidative phosphorylation (OxPhos), are significantly enriched in the HRD‐high group. Furthermore, a wide range of immune cell activation signatures is enriched in HRD‐high cases of high‐grade serous ovarian cancer (HGSOC). On further cell‐type‐specific analysis, M1‐like macrophage genes are significantly enriched in HRD‐high HGSOC cases, whereas M2‐macrophage‐related genes are not. The immune‐response‐associated genomic features, including tumor mutation rate, neoantigens, and tumor mutation burdens, correlated with HRD scores. In conclusion, the results of this study highlight the biological properties of HRD, including enhanced energy metabolism, increased tumor neoantigens and tumor mutation burdens, and consequent exacerbation of immune responses, particularly the enrichment of M1‐like macrophages in HGSOC cases.