PDCD1 and neoplasm: These “don't eat me” signals interact with the corresponding receptors on phagocytes surface, including signal regulatory protein α (SIRP α), programmed cell death 1 (PD-1), leukocyte immunoglobulin-like receptor 1 (LILRB1), Siglec-10, etc. The interaction between these receptors and ligands promotes the tumor to escape the phagocytosis of phagocytes.