The present application relates generally to genetically modified arenaviruses that are suitable vaccines against neoplastic diseases, such as cancer. The arenaviruses described herein may be suitable for vaccines and/or treatment of neoplastic diseases and/or for the use in immunotherapies. In particular, provided herein are methods and compositions for treating a neoplastic disease by administering a genetically modified arenavirus in combination with an immune checkpoint inhibitor, wherein the arenavirus has been engineered to include a nucleotide sequence encoding a tumor antigen, tumor associated antigen or antigenic fragment thereof. Figure 1
