Background: Genetic events cannot account for the complexity of human carcinogenesis alone. Mutations of epigenetic regulators and aberrations of their expression patterns have been detected in various human malignancies. Methylation of histone H3 at lysine 4 (H3K4me), is an evolutionarily conserved histone modification that marks regions of active transcription and regulates cell growth, migration, and invasion. The MLL/KMT2 family of histone methyltransferases specifically methylate histone H3 at lysine 4. Objective: The aim of this study was to explore the role of KMT2C/MLL3 as well as key histone modification activating markers, such as H3K4me2 and H3K4me3 in a cohort of surgically resected human lung adenocarcinomas in an effort to reveal possible biomarkers for lung adenocarcinoma diagnosis and prognosis and potential therapeutic targets. Method: The immunohistochemical expression of KMT2C/MLL3, H3K4me2 and H3K4me3 was analyzed in formalin fixed paraffin embedded tissue from 96 patients with lung adenocarcinoma. Results were associated with clinicopathologic parameters and patient’s prognosis. Results: Nuclear expression of KMT2C/MLL3 in epithelial cells was independently associated with shorter overall survival. Cytoplasmic H3K4me2 expression was associated withT stage and nuclear H3K4me2 expression was associated with female gender and patients’ prognosis. The latter association persisted after multivariate analysis. No association was found between H3K4me3 expression and clinicopathological data or disease outcome in our cohort of patients. Conclusion: These results suggest that the pattern of histone modifications and KMT2C/MLL3 expression can be used as an independent prognostic factor in lung adenocarcinoma, revealing that chromatin remodeling is criticallyinvolved in cancer progression.