Landscape of DNA damage response gene alterations in breast cancer: A comprehensive investigation

DNA damage response (DDR) gene alterations are prevalent in breast cancer (BC) and important for treatment decisions. Intensive studies on DDR alterations in BC are still needed.The authors included 438 patients with metastatic breast cancer from their next-generation sequencing database and 1091 patients with early-stage breast cancer from The Cancer Genome Atlas (TCGA) database in the analysis to characterize molecular alterations in the DDR pathway.Germline DDR mutations were more prevalent in younger patients and those with HER2-negative cancers. Tumors with germline DDR mutations more commonly had somatic DDR mutations, especially those with germline Fanconi anemia (FA) pathway mutations. Notably, 66.67% (four of six) of patients with germline PALB2 mutations had tumors that harbored somatic PALB2 mutations. No differences in prognosis were observed in patients with germline or tumor somatic DDR mutations compared to patients and tumors that were wild-type. Compared to early BC, the frequency of somatic DDR mutations in metastatic cancers was significantly higher (24.89% vs. 16.02%, p < .001). Higher tumor mutation burdens were observed in cancers with somatic DDR mutations, but not in cancers with germline DDR mutations. Furthermore, tumors with somatic DDR mutations showed an abundance of anticancer immunological phenotypes. Somatic FA and mismatch repair pathway mutations were associated with increased expression of immune checkpoint molecules. Although most DDR genes were significantly positively associated with expression of proliferation-related genes, PARP3 expression was negatively correlated with MKI67 expression. Lower PARP3 expression was associated with a worse prognosis in TCGA database by multivariate Cox analysis.Patients with germline FA mutations more frequently have tumors with somatic DDR mutations. Somatic DDR mutations lead to anticancer immunological phenotypes in BC. No differences in prognosis according to germline or somatic DDR mutations were found.