Cancer is a serious health problem in the world and is one of the diseases with high morbidity and mortality. Although chemotherapy and/or radiotherapy is the primary treatment option for cancer patients, it is an inevitable fact that chemotherapeutic agents also have serious side effects risks (Sameiyan et. al. 2019). Therefore, the emergence of new treatment strategies is of great importance in terms of treatment options to be offered to patients. One of these treatment strategies is cancer immunotherapy. Cancer immunotherapy is a treatment approach developed to increase the specificity and potency of immune system cells against cancer and is an important signaling pathway targeted in PD-1/PD-L1 immunotherapy (Salmaninejad et. al. 2019). In this study, the programmed cell death protein (PD) 1 and PD-1 ligand (PD-L1) pathways and their role in cancer immunotherapy were discussed in detail.