||Aim and objectives. The aim of this study was to assess epigenetic and genetic alterations of non-coding genome structures and their significance in the pathogenesis of gastric cancer. Objectives: 1. To evaluate the alteration of miR-137 gene expression and promoter methylation status and its implication for gastric cancer and prema-lignant gastric lesions. 2. To perform a comprehensive analysis on LINE-1 methylation level in different stages of gastric carcinogenesis and to evaluate its prognostic potential. 3. To assess the association between single nucleotide polymorphisms of miR-27a, miR-146a, miR-196a-2, miR-492, miR-608 genes and gastric cancer or premalignant gastric lesions. Relevance and novelty of the study Current study provides: 1) novel evidence on epigenetic and genetic alterations of miR-137 in gastric carcinogenesis; 2) comprehensive LINE-1 methylation analysis and its prognostic potential in GC; 3) novel insights into the implication of genetic variants of miRNA genes and their association with GC and high risk atrophic gastritis. All of the analyses were performed in a cohort of patients of European descent, which, in the whole context of existing literature on current issues, emphasize differences in GC pathogenesis based on subjects’ ethnicity. Moreover, all three studies included a set of patients with premalignant gastric lesions (chronic/atrophic gastritis) which was not frequently investigated in analogous studies. Even-tually, our results contribute to the overall molecular basis of gastric cancer pathogenesis and may be employed as a reference data for scientific studies in the future.