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e20542 Background: Lung cancer is the most common malignant tumor after breast cancer and is the main cause of cancer mortality. Mutations in the EGFR gene typical of lung cancer lead to constitutive activation of the epidermal growth factor receptor and malignant cell transformation. The purpose of this study was to identify associations between double and triple mutations in EGFR and clinical and pathological characteristics of patients in the South of Russia diagnosed with lung cancer. Methods: DNA was extracted from FFPE samples of 240 patients. Mutations in EGFR were detected using Cobas EGFR Mutation Test detection kit (Roche). Results: The mutant type of EGFR was identified in 24.6% of cases, and the most common activating mutations were ex19del (47.5%) and L858R (30.5%). Insertion in exon 20 was detected in 5.1% of mutation cases, G719X - in 3.4%. We also registered cases of identification of two or three mutations in one tumor: ex19del - L858R, ex19del - T790M, L858R - T790M with a frequency of 3.4% and G719X - ex20ins, ex19del - L858R - ex20ins with a frequency of 1.7%. Similar frequency is characteristic of the Caucasoid population of the USA. Multiple mutations in EGFR are associated with early manifestations of lung cancer and rapid progression of the disease. Two patients with two mutations EGFR T790M and L858R were of particular interest. According to the literature data, T790M is the most common somatic mutation that causes resistance to targeted therapy; however, rare cases could be associated with germinal variation of T790M. The primary T790M mutation is more common in patients with two or three mutations in EGFR. Conclusions: Mutations in the EGFR gene were detected in 24.6% of lung cancer cases in a patient population in the South of Russia. The frequency of two or three mutations in the EGFR gene was 0.33%. The timely detection of these mutations is particularly important for family cases when the risk group can be determined.

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