Located in the upper abdominal region, the stomach is a J-shaped organ that is made up of five different layers. Stomach cancer -- also known as gastric cancer -- can develop in any part of the stomach. Most stomach cancers begin in the mucosa, which is the innermost layer.
While believed to develop slowly over many years, stomach cancer is usually preceded by precancerous changes in the stomach lining. These changes rarely produce symptoms. Stomach cancer often does not cause symptoms until it is advanced; only about 10 to 20 percent of stomach cancers are detected in their earliest stages.
Approximately 21,260 Americans are diagnosed with stomach cancer each year. This kind of cancer develops most often in people over the age of 65 and is more common in men than in women. Stomach cancer is much more common in certain regions of Asia, Central Europe, and Central and South America, possibly due to dietary factors.
The incidence of stomach cancer has decreased significantly in the US since the 1930s, which may be due to the increased use of refrigeration for storing food and the subsequent decrease in the consumption of salted and smoked foods (which can contain cancer-causing nitrates). However, there is an increasing incidence of cancers that involve the upper end of the stomach and the junction of the esophagus, particularly in white men, for reasons that are unknown.
Types of Stomach Cancer
Most stomach cancers (90 to 95 percent) are adenocarcinomas, which begin in cells that line the stomach. Other less common types of stomach cancer include lymphoma (cancer that begins in cells of the immune system); gastrointestinal stromal tumors (cancer of the muscle or connective tissue of the stomach wall, also known as GIST); and carcinoid tumors (cancer of the hormone-producing cells of the stomach).
The remainder of this cancer information overview focuses on stomach adenocarcinomas.
