PDCD1 and neoplasm: Additionally, PD-1/PD-L1 inhibitors rely heavily on the tumor microenvironment to work; theoretically, only a fraction of patients with inflamed tumor could benefit from immunotherapy, and other immune types such as the immune-desert phenotype and immune-excluded tumors have poor response partly due to the absence of immune effector cells in the tumor microenvironment or obstruction between the immune effector cells and tumor cells [15].