Different types of stomach cancer include:

Adenocarcinomas of the stomach develop in the cells of the innermost lining of the stomach. Most stomach cancers are classified as adenocarcinomas of the stomach.

Lymphoma is a cancer of the immune system tissue that may start anywhere lymph tissues are found, including the stomach. Lymphomas in the stomach are rather rare and only account for about 4 percent of all stomach cancers.

Gastrointestinal stromal tumors, or GISTs, are a rare type of stomach cancer that forms in a special cell found in the lining of the stomach called interstitial cells of Cajal (ICCs). Under a microscope, GIST cells look similar to muscle or nerve cells. These tumors may develop throughout the digestive tract, but about 60 to 70 percent occur in the stomach.

Carcinoid tumors typically start in the hormone-producing cells of the stomach. These tumors usually do not spread to different organs and account for only about 3 percent of stomach cancer incidence.

Gastric carcinoid tumors come in three types:

• Type I and II ECL-cell carcinoids rarely spread to other parts of the body and may produce no symptoms. They are most often discovered during an endoscopy for another health issue, such as acid reflux.
• Type III ECL-cell carcinoids are more aggressive. The excess hormone secretion of carcinoid tumors may lead to a condition called carcinoid syndrome, marked by flushing, abdominal pain, diarrhea, constriction of the bronchial tubes in the lungs and, in some cases, heart troubles like valve dysfunction. Carcinoid syndrome is a sign that more aggressive treatment may be required.

Next topic: What are the stages of stomach cancer?