Like other solid tumors, pulmonary carcinomas have developed several mechanisms by which they escape the attack of cytotoxic immune cells. Some of these mechanisms have recently gained special attention: the programmed death 1—programmed death ligand 1 and 2 (PDL1/2-PD1) and the CTLA4 system. Tumor cells as well as lymphocytes can express ligands for PD1. By this they interact with surface molecules on CD8+ T cells causing apoptosis and furthermore influence also the microenvironment via orchestration by specific cytokines, which altogether cause immune tolerance. Therapy using antibodies against PDL1 has shown significant improvement experimentally as well as in clinical studies to restore the cytotoxic attack of T lymphocytes towards tumor cells in several solid malignancies. Parallel to targeting PDL1 by anti-PDL1 antibodies, also antibodies against the receptor PD1 have been created and used experimentally and in clinical trials with success. In some clinical trials specific immunohistochemistry tests for the expression of PD1 and PDL1 were used to select those patients, who might best respond to the antibody-based therapy. A strong staining in at least 5% of tumor cells and/or lymphocytes—or 50% in another trial—was regarded as a positive result and predictive for outcome. Looking up clinical data of these trials, it is evident that the majority of patients are detected by this simple stain. However, there exists also a not-to-be-neglected number of patients, who do not respond to treatment although being positive for PD1/PDL1, as well as patients who do respond despite being negative or low positive for these molecules. Several resistance and immune escape mechanisms have been detected. Some of these mechanisms are based on metabolic reprogramming of tumor cells and cells of the tumor microenvironment. Further immune checkpoint molecules have been detected, and some of these are currently in clinical studies tested. In addition, the composition of the tumor stroma has gained considerable attention, such as CD4 and CD8 lymphocytes, and antigen-presenting dendritic cells. Moreover, the spatial position of the immune cells is likely most important in this respect.