Gastric cancer is one of the most frequent cancer type in the world today. This fact emphasises the importance of identification of useful diagnostic and prognostic markers for gastric cancers in their earliest stages. Aim of this review is to summarize the genetic knowledge related to gastric carcinogenesis and progression and to offer a survey of the gene expression pattern changes and their functional classification. Microarray results show that the gene expression pattern detected in gastric cancers highly depends on the histological type and heterogeneity of the sample, array type and data analyzing softwares. Recent experiments point out the changes of not just the alterations of tumor suppression, apoptosis, cell cycle regulation and signal transduction, but tumor cell metabolism and cell-microenvironment interactions, too. All results show connection to and complete the already known molecular background of gastric cancer.