The Evolution of Immunotherapy Against Tumors: An Historical Approach summarizes the literature concerning the development of the theory of immune surveillance against tumors. It discusses the evidence for and against this theory, along with the concept of immunoediting. Finally, current approaches in anti-tumor immunotherapy will be analyzed. The immune system plays a major role in the surveillance against tumors. To avoid attack from the immune system, tumor cells develop different strategies to escape immune surveillance. Evidence of immune surveillance comes from both animal models and clinical observations. Mice with a wide variety of immunodeficiencies have a high rate of tumor incidence and are more susceptible to transplanted or chemical carcinogen-induced tumors. Immunosuppressed patients have a high incidence of tumors. However, many patients develop cancer even in the presence of an apparently normal immune system. This indicates that tumor cells can escape immune surveillance.