Gastric cancer remains highly prevalent and accounts for a notable proportion of global cancer mortality and this is associated with poor survival rates. Understanding the molecular genetic changes of gastric carcinoma may offer an insight into its pathogenesis helps in identifying new biomarkers, aid prognostication, and novel treatment targets. Over a past few decades, advances in technology and high throughput analysis have improved understanding of the molecular genetic aspects of gastric cancer. In this article, hierarchy of the changes at genetic and molecular level including several aspects which are heterogenous and represents a wide spectrum such as tumor suppressor genes, oncogenes, cellcycle regulators, apoptosis, cell-adhesion molecules, loss of heterozygosity, microsatellite instability, and epigenetic changes. The classification of gastric carcinoma at molecular and genetic level as well as hereditary gastric carcinoma is elaborated. The molecular genetic aspects regarding pathogenesis, changes and aberrations of all genes and pathways which are involved in gastric cancer are addressed in this review.

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Background: The aryl hydrocarbon receptor repressor (AHRR), a member of the growing superfamily, is a basic helix-loop-helix/PerAHR nuclear translocator (ARNT)-Sim (bHLH-PAS) protein. AHRR has been proposed to function as a putative new tumor suppressor gene based on studies in multiple types of human cancers. This current study aims to investigate AHHR expression and its prognostic significance in gallbladder cancer. Methods: The study includes 48 gallbladder cancer and 34 chronic cholecystitis cases as controls. The expression level of AHRR was analyzed by using semi-quantitative PCR and immunohistochemical staining. The results were correlated with different clinical parameters. Results: We demonstrate that the expression of AHRR is significantly down-regulated in gallbladder cancer tissue samples as compared to that in chronic cholecystitis tissue samples by reverse transcriptase PCR (RT-PCR) ( P = 0.017) and immunohistochemistry analysis ( P = 0.002). Interestingly, our RT-PCR data revealed that AHRR mRNA expression is frequently down-regulated (45.8%; 22/48) in cases as compared to 14.7% (5/34) in controls. Similarly, immunohistochemical analysis data show significant down-regulation of AHRR expression in 77.1% (37/48) of gallbladder cancer cases than 44.1% (15/34) in controls ( P < 0.017). Reduced mRNA and protein expression is significantly associated with advanced T-stage ( P = 0.001), histological differentiation ( P = 0.001), and tumors with nodal metastasis ( P = 0.001). Decreased expression of AHRR is significantly associated with poor prognosis in gallbladder cancer patients. Conclusion: In conclusion, the present study suggests that low AHRR expression may be critical in gallbladder cancer development. Our data suggests that AHRR may act as a tumor suppressor gene and its expression profile may be useful as a diagnostic marker in gallbladder cancer.