High PARP7 Expression is Associated with Higher Estrogen Response and Immune Suppression but Less Cell Proliferation and Better Survival in Breast Cancer

Various poly(ADP-ribose) polymerases (PARPs) are known to be related to DNA repair, and PARP7 has been linked to estrogen signaling and immunity. Recently, PARP7 was shown to increase cancer cell proliferation, but reports are conflicting. Given that these studies are mostly based on in vitr o experiments, this study investigated how PARP7 expression impacts breast cancer patients. Clinical and transcriptomic data of breast cancer patients were obtained from the METABRIC ( n = 1904), TCGA ( n = 1090), and SCAN-B ( n = 3069) cohorts. The median value was used to divide the cohorts into high- and low-PARP7 groups. High PARP7 expression was significantly associated with better overall survival in two of the three cohorts ( p < 0.05), and PARP7 was expressed predominantly by epithelial cells ( p < 0.001). Estrogen receptor (ER)-positive breast cancer had a higher expression of PARP7 than other subtypes ( p < 0.001). High PARP7 expression was associated with high estrogen and androgen response consistently in all cohorts. Tumors expressing higher PARP7 levels had significantly lower mutation rates, neoantigens, type 1 interferon (IFN-1), and immune cell infiltration in ( p < 0.001). High PARP7 expression was associated with less enrichment of cell proliferation-related gene sets (E2F targets, G2M checkpoint, and MYC targets), in all cohorts. Higher PARP7 expression was associated with less cancer cell proliferation, lower tumor grade, and lower Ki67 ( p < 0.001). High PARP7 expression is associated with estrogen and androgen response, but also with better overall survival and lower cell proliferation.