NCI: An adenocarcinoma arising from the stomach glandular epithelium. Gastric adenocarcinoma is primarily a disease of older individuals, most commonly develops after a long period of atrophic gastritis and is strongly associated with Helicobacter pylori infection. The lack of early symptoms often delays the diagnosis of gastric cancer. The majority of patients present with advanced tumors which have poor rates of curability. Microscopically, two important histologic types of gastric adenocarcinoma are recognized: the intestinal and diffuse type. The overall prognosis of gastric adenocarcinomas is poor, even in patients who receive a "curative" resection (adapted from Sternberg's Surgical Pathology, 3rd ed., 1999).