We therefore hypothesized that the combination of anti-PD-L1 and anti-CTLA-4 antibodies, having non-redundant mechanisms for antitumor immune systems [25], with X-ray irradiation would provide a higher probability of the abscopal effect for osteosarcoma, which is known as an X-ray-resistant neoplasm. Here, CTLA4 is linked to osteosarcoma.