Gastric (stomach) cancer is a disease in which malignant (cancer) cells form in the lining of the stomach. The stomach is in the upper abdomen and helps digest food.
Almost all gastric cancers are adenocarcinomas (cancers that begin in cells that make and release mucus and other fluids). Other types of gastric cancer are gastrointestinal carcinoid tumors, gastrointestinal stromal tumors, and lymphomas.
Infection with bacteria called H. pylori is a common cause of gastric cancer. Gastric cancer is often diagnosed at an advanced stage because there are no early signs or symptoms.