Figure 1 presents the relative frequency data for these gene mutations in BTC, extracted from the COSMIC/TCGA database. PARP inhibitors (PARPi) are the first group of drugs designed to exploit cancer HRD. Preclinical studies suggest that BTC is susceptible to PARP inhibition. Several PARPi, including olaparib, rucaparib, and niraparib, are under clinical investigation in BTCs [24]. This evidence concerns the gene PARP1 and cancer.