Standard anti-cancer therapeutic modalities like chemotherapy and radiotherapy evoke host's reactions that include involvement of the immune system. Elucidation of these mechanisms offers the double advantage of enabling a more rational choice of cytotoxic therapy and exploring the combination with immunotherapy. Radiotherapy, a well established local anti-cancer approach, is a particularly interesting partner for immunotherapy, since it can be harnessed to specifically modify the immunogenicity of the primary tumor and its microenvironment, in the attempt to generate an in situ immunization of the host against a patient's own cancer.