The primary mission of the Gastric Histopathology Core is to provide high quality, rapid-turnaround immunohistochemistry and specialized research histology services to investigators in this PPG, and to provide expert histopathologic interpretation, through collaboration with Dr. Kay Washington and Dr. M. Blanca Piazuelo. The following services are proposed: 1. To provide expert evaluation of histopathology of rodent models of H. pylori-induced gastric neoplasia and correlation with human disease 2. To provide expertise in developing, performing and evaluating immunohistochemical studies on animal tissues, with robust quality control measures, and with extension to human tissue if needed 3. To provide laser microdissection services 4. To provide tissue microarray services and access to human gastric tissue samples as needed The three component projects and Core B (Proteomics Core) of this proposed Program Project all rely heavily upon morphologic analysis of gastric tissues isolated from rodent models of Helicobacter pylori-induced gastritis and gastric neoplasia. Dr. Washington's and Dr. Piazuelo's expertise in interpretation of histopathologic changes in rodent models and in interpretation of immunohistochemical studies will be critical to this work, and these collaborative activities are currently not funded through existing resources. By utilizing the resources of an Gl research-related immunohistochemistry facility, it will be possible to achieve high standards for all histologic studies proposed in this grant. This centralization of histologic services under the supervision of experienced pathologists with a dedicated interest in gastrointestinal pathology will allow careful attention to quality assurance.