Increasing the efficiency of antitumor therapy is one of major relevant tasks of oncology today. During recent years experimental evidence for active involvement of immune system in the regulation antitumor effects of cytostatic thereby has been obtained and theoretically justified. It was demonstrated that efficient cytostatic treatment is related to the cytotoxic activities of immune cells targeted against tumor cells. Such cytotoxic activities of immune cells are induced by radiotherapy or chemotherapy, where both innate and adaptive immune mechanisms are involved. However the disturbance in the functions of immune system can result in the impaired efficiency of cytostatic anti-tumor therapy. Cytotoxic agents can affect immune reactions by increasing the antigenic properties of tumor cells, facilitating their recognition of immune system, by stimulation of functional activation effector immune cells, elimination of immunosuppressive factors as well as systemic effects of antitumor therapy. A consideration of the crucial role of immune system in the providing of the efficiency of cytostatic antitumor therapy develops novel therapeutic approaches for treatment of malignant disorders based on balanced synergistic action of cytostatic agents and innovative immunomodulatory approaches.