When used in combination with chemotherapy and radiotherapy, OVs may assert synergistic effect and significantly enhance the anti-tumor effect, especially when combined with immunotherapy such as immune checkpoint inhibitors like anti-CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) antibody and anti-PD-L1/PD-1 antibody (18). Here, CTLA4 is linked to neoplasm.