Cytokine-induced killer cell, CIK, a new type of immunocompetent cells, CIK is strong in proliferation and cytotoxicity. The cells are featured in recognizing tumor cells, such as missiles, which can precisely attack tumor cells, without harming normal cells, improve the immune system and immunity, especially with significant results for patients after surgery or radiotherapy and chemotherapy, which could eliminate residual metastatic lesions, prevent cancer cell proliferation and relapse, enhance immunity, thus is considered the one of the top choices for the next generation of immunotherapy.