In this thesis, there is an overall review of some malignant disease theories, e.g. the problem of circulating tumor cells and cancer cell dormancy. The importance of tumor microenvironment is explained, thus the logic of immunotherapy. A detailed description can be read about the CTLA-4 checkpoint pathway and the PD-1 checkpoint pathway. The therapies in focus are the immune checkpoint inhibitors. Finally, some future treatment perspectives can be read.