Stomach Cell
The vast majority of cancers that originate in the stomach--about 95 percent--are adenocarcinomas, which develop from the epithelium, the inner lining of the stomach. Adenocarcinomas fall into two classifications--intestinal or diffuse. Intestinal stomach cancer features large cells that attach to each other to form well-defined tubular structures. In diffuse stomach cancer, the cells are smaller, clustering together to attack the lining of the stomach. These cellular clusters do not have a well-defined border. Diffuse stomach cancer typically strikes younger people.

Approximately 5 percent of stomach cancers are gastric lymphomas. Gastric lymphomas develop from the lymphatic system in the stomach. They can sometimes be difficult to differentiate from adenocarcinomas, but making this distinction is crucial in that they behave clinically in a very different fashion. Other forms of stomach cancers include, leiomyosarcoma which develop in the muscle tissue. Other rare forms of stomach cancer are adenoacanthomas, squamous cell carcinomas, lymphomas, small cell carcinomas, carcinoid tumors and Kaposi's sarcoma.

Cancer that develops in the stomach may metastasize (spread) throughout the stomach and into other organs, grow along the stomach wall into the small intestine or esophagus, or extend through the stomach wall to invade nearby lymph nodes, the pancreas and the colon. Cancer cells can also migrate to distant locations such as the ovaries.