Diagnostic value of immunocytochemical antibodies in lung tumor diagnostics Study Objectives: This study aims to research the frequency of different lung tumor subtypes and determine the diagnostic value of immunocytochemical antibodies for TTF-1, p40, CD56 and CK 5/6 in lung tumor diagnostics. Study Design: The study is designed as a cross-sectional study with historical data, which analyzed participants within the previous five years. Participants and Methods: The participants included in the study were all who, in the period between January 1st 2019 and December 31st 2023, at the Clinical Institute of Cytology and the Clinical Institute of Pathology of the Clinical Hospital Center in Osijek, were pathohistologically positive for any malignancy in the lung or had a positive molecular testing result. Discovered results were statistically analyzed and presented in tables. Results: 313 participants were included in the study. Adenocarcinoma, squamous-cell carcinoma and small-cell lung cancer were the most diagnosed. Lung carcinoma was more common in men, although adenocarcinoma is an exception to this, with 46 % affected women and 34 % affected men. Adenocarcinoma showed above 80 % positivity for TTF-1, squamouscell carcinoma above 70% for p40 and above 90 % for CK 5/6, and small-cell lung carcinoma above 90 % for both TTF-1 and CD56. 12 % of the tested participants were positive for an EGFR mutation, out of which the majority has adenocarcinoma and majority were women. Conclusions: Most frequently diagnosed lung tumors are adenocarcinoma, squamous-cell carcinoma and small-cell lung cancer. There are significant differences in the distribution of patients in regards to immunocytochemical antibody testing and pathohistological diagnoses. The mutation of EGFR is generally tied to the origination of adenocarcinoma and is more frequently found in women.