More than 90 percent of stomach cancers are adenocarcinomas that originate in the glandular cells in the mucosa of the stomach’s inner lining, according to the American Cancer Society (ACS). Types of adenocarcinoma of the stomach include:

• Type 1. This cancer forms in the cells of the stomach closest to the duodenum (beginning of the small intestine). This cancer is associated with infection with H. pylori bacteria and a diet high in certain foods, such as smoked meats.
  
  
• Type 2. This less common type is linked to genetic factors. All the cells of the stomach can be affected. This type is also much more aggressive than type 1, and can quickly grow and spread to the lymph nodes, pancreas, liver and colon.

Rare types of stomach cancers include:

• Lymphomas. Cancer that affects the immune system cells along the stomach wall. According to the ACS, lymphomas account for 4 percent of stomach cancers. The growth rate of lymphomas varies. Mucosa-associated lymphoid tissue (MALT) lymphomas are often associated with H. pylori infection and may be curable if discovered in the early stages.
  
  
• Carcinoid tumors. Tumors that originate in the stomach’s hormone-producing cells. These tumors are rare and grow and spread slowly to other tissues in the body. According to the ACS, these tumors represent about 3 percent of stomach cancers.
  
  
• Gastrointestinal stromal tumors (GISTs). Rapid-growing tumors that spread quickly to other areas and do not respond well to standard treatment. These rare tumor cells originate from interstitial cells of Cajal, which are part of the autonomic nervous system. GISTs can be found throughout the gastrointestinal tract, but are most common in the stomach.