Immunotherapy is a relatively new method of treatment used in oncology. Cancer immunotherapy, also known as immuno-oncology (IO), is a form of cancer treatment, which revolutionized the field of oncology and is constantly developing. Several monoclonal antibodies (mAbs) directed against cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein 1 (PD-1), or programmed cell death ligand 1 (PD-L1) have been approved both as a single agent and in combination with other drugs for the treatment of patients with different cancers. The first approved immune checkpoint inhibitors (ICIs) were ipilimumab (anti-CTLA-4) in 2011, pembrolizumab (anti-PD-1) and nivolumab (anti-PD-1) in 2014 (Available on: www.fda.gov ). The PD-1/PD-L1 pathway is the most often targeted axis in IO. Anti-PD-1 drugs target a checkpoint PD-1 protein on the surface of T lymphocytes cells (Alsaab et al. 2017). By binding with the PD-1 receptor they are blocking interaction with PD-L1 & programmed cell death 1 ligand 2 (PD-L2), leading to activation of T cell lymphocytes and exposing tumor to an immune assault (Alsaab et al. 2017).