PDCD1 and cancer: The cancer immune microenvironment has been intensively studied in the past few decades, paving the way for the recent clinical application of immunotherapies targeting immune checkpoints such as cytotoxic T‐lymphocyte associated protein 4 (CTLA4), programmed cell death 1 (PDCD1/PD1), and programmed cell death 1 ligand 1 (CD274/PDL1) 1, 2.