Objectives: The aim of this paper is to present detailed molecular testing which solidifies the status of the EGFR gene as a predictive biomarker in patients with lung cancer for the purpose of applying targeted therapy in their treatment. Material and methods: The material used for analysis can be blood or tumor tissue of operated patients.Procedures for DNA isolation, measurement of DNA concentration and detection of EGFR mutations with the help of commercially available kits are described. Results: The results obtained by detecting EGFR gene mutations are processed by software and ultimately a report is obtained that shows in detail all detected mutations in the patient's sample. Conclusion: Molecular testing of the EGFR gene, i.e. detection of mutations in patients with lung cancer, is important in order to determine the correct targeted therapy. In order to determine the presence of mutations, it is necessary to isolate DNA from a blood sample or from the patient's tumor tissue, and then multiply and detect it. Patients with the presence of pathogenic mutations in the EGFR gene are candidates for targeted therapy.