Figure 1. Tumor as an “altered self” or “immunoprivileged self” entity. The hypothesis that self epitopes are abundant in the antigenic repertoire of tumor cells is based on the facts that tumor-specific antigens (TSAs) are difficult to identify and that antitumor immune responses often target self antigens. Blue dashes depict the immunosuppressive microenvironment that is often associated with tumors. Oval areas reflect overall tumor burdens and do not necessarily represent individual tumor sites. Ab, antibody; TIC, tumor-initiating cell.