CEACAM1 and neoplasm: By secreting cytokines, chemokines or growth factors, as well as up-regulating specific surface receptors, e.g., PD-L1, CTLA-4, carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), and others, tumor cells become competent in dampening and finally escaping the immune system (Figure 1) [79,80,81,82,83,84].