CTLA4 and lung cancer: Immune evasion through upregulation of immune checkpoints such as indoleamine 2,3-dioxygenase (IDO1), cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death-ligand 1 (PD-L1) has been identified as an evolutionary trajectory during pre-invasive stages of lung cancer (15).