TTF1 and non-small cell lung carcinoma: Another aim of the study was to determine the level of expression and localization of PD-L1 ligand in NSCLC and to compare it with the expression level of commonly used diagnostic markers such as Ki-67 proliferation antigen, p63 and thyroid transcription factor 1 (TTF-1) proteins, which are routinely used to distinguish a morphological subtype of NSCLC.