Carcinoma of the stomach is one of the most prevalent cancer types in the world today. Only a limited number of biomarkers are available for detection and prognostic evaluation of gastric cancer. New advances in identifying molecular biomarkers are essential. Two major forms of gastric cancer are distinguished according to their morphological and clinicopathological classifications (well-differentiated/intestinal type and poorly differentiated/diffuse type)--characteristics that can also be attributed to different oncogene activations. Many genes related to cell cycle regulation and signal transduction have been implicated in gastric cancer progression. In particular, there is convincing evidence that protein tyrosine kinases (PTKs) are involved in oncogenesis and disease progression. To learn more about the biological significance of all expressed PTKs in human cancers, an improved and more-comprehensive PTK profiling approach has been developed to discover additional PTKs activated in cancer cells. With the completion of the human genome project and the availability of cDNA microarrays or DNA chips, the entire human transcriptome can be used for elucidating genes responsible for human gastric cancer oncogenesis and progression.