PARP1 and neoplasm: To date, preclinical studies revealing the therapeutic efficacy of the IR plus PARP inhibition combination have been conducted in subcutaneous tumours, whether BRCA-deficient or BRCA-proficient, and the vast majority of these studies used a 2-Gy fractionated irradiation regimen.14–16,18,20–23,25,28,31 The benefit of this combination was confirmed in an orthotopic tumour model, a pancreatic xenograft of the MiaPaca-2 cell line.30 However, these studies were conducted with human tumour models grafted in immunocompromised mice.