It was reported by the following mechanisms [6]: (i) the expressions of tumor antigens were absent or decreased on the surface of tumor cells; (ii) the expressions of major histocompatibility complex (MHC) class I molecules on the tumor cells were reduced to a very low level; (iii) the tumor cells expressed FasL, which induced the apoptosis of lymphocytes that expressed Fas; (iv) the expressions of costimulatory signal molecules were absent in tumor cells; and (v) tumor cells could produce cytokine or hormone, such as IL-10, which inhibited organism immune function. The gene discussed is FAS; the disease is neoplasm.