HDAC9 and cancer: Moreover, HDACis downregulate key DNA damage‐repair proteins, including BRCA1, BRCA2, and RAD51, which have been validated in various cancer types, and HDACi treatment sensitizes cancer cells to the lethal effects of PARPis.[32, 45] Building on these findings, we developed bifunctional HDAC and PARP inhibitors, with the lead compound P2 effectively restoring STING signaling and triggering a robust tumor‐intrinsic immune response.