Numerous preclinical studies have previously demonstrated that PARP or ATR inhibition radiosensitises human cancer cells in vitro, and improves RT efficacy in vivo in human tumour models xenografted subcutaneously into immunodeficient mice.14–31 In this study, LL2-luc Lewis lung carcinoma murine tumour cells were implanted either subcutaneously or orthotopically. Here, ATR is linked to cancer.