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Cancer Health Center

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Understanding Stomach Cancer -- the Basics

What Is Stomach Cancer?

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 (about 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).
  • Other types include carcinoid, small cell carcinoma, and squamous cell carcinoma.
  • Metastatic cancers from breast cancer, melanoma, and other primary sites of cancer are also seen in the stomach.

Stomach Cancer

The number of stomach cancer cases has declined over the past 60 years. Even though it is now the 16th most common cancer in the U.S., stomach cancer is still a leading cause of cancer deaths in other parts of the world. The exact cause of stomach cancer is unknown, but most are believed to result from exposure to carcinogens (various cancer-causing agents), especially nitrates. Nitrates are 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.

Various medical conditions are associated with an increased risk of developing stomach cancer. These include:

Helicobacter pylori (H. pylori) infection of the stomach lining is associated with gastric lymphoma and adenocarcinoma. H. pylori is a bacterium that infects the lining of the stomach and causes chronic inflammation and ulcers. The risk of developing cancer, in the presence of an infection with this bacteria is low. This bacterium can be found in up to two-thirds of the world’s population. In persons infected with this bacterium, the risk of developing gastric cancer is thought to be up to six times that of non-infected persons.

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