Cancer of the stomach, or gastric cancer, is a disease in which stomach cells become malignant (cancerous) and grow out of control, forming a tumor. Almost all stomach cancers (95%) start in the glandular tissue that lines the stomach. The tumor may spread along the stomach wall or may grow directly through the wall and shed cells into the bloodstream or lymphatic system. Once beyond the stomach, cancer can spread to other organs.

Stomach cancers are classified according to the type of tissue in which they originate.

• Adenocarcinomas -- the most common -- start in the glandular stomach lining.
• Lymphomas develop from lymphocytes, a type of blood cell involved in the immune system.
• Sarcomas involve the connective tissue (muscle, fat, or blood vessels).

Although the number of stomach cancer cases has declined over the past 60 years, it is still the seventh leading cause of cancer death in the U.S. The exact cause of stomach cancer is unknown, but most are believed to result from exposure to carcinogens (various cancer-causing agents), especially nitrates -- substances found in prepared foods (especially meats) that are dried, smoked, salted, or pickled. Carcinogens cause errors in the genetic code that controls growth and repair of cells.

Stomach cancer can often be cured if it is found and treated at an early stage, however, it is usually diagnosed at a later stage. Unfortunately, the outlook is poor if the cancer is already advanced.

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