Although cancer immunotherapy, which is able to target specifically cancer cells without detrimental effects to normal cell functions, would serve as an ideal therapeutic modality, most of the randomized clinical trials of cancer immunotherapy have not demonstrated a meaningful survival benefit to cancer patients over preexisting therapeutic modalities. Due to the discrepancy between the impressive preclinical results and the limited clinical results, the cancer immunotherapy is not accepted generally as a standard therapy for cancers. A variety of immune escape mechanisms are thought to be involved in this ineffectiveness of cancer immunotherapy. Therefore, elimination of immunosuppressive activities in tumor microenvironment will enhance the effectiveness of cancer immunotherapy, which is currently focused on activation of tumor-specific immune responses. Since there are now increasing evidences showing that many cytotoxic anticancer drugs including targeted agents given in lower-than-therapeutic doses have not only the ability to eliminate tumor cells but can also block the immunosuppressive activities in tumor microenvironments and consequently favor the development of anticancer immune responses, clinically available drugs can be considered for their rapid application to cancer immunotherapies to enhance the efficacy of cancer immunotherapies with marginal effects on cancer treatment.
Keywords: Anticancer drugs; cancer immunotherapy; immunosuppressive microenvironments.