Gastric cancer is cancer that starts in the stomach.

Several different types of cancer can occur in the stomach. The most common type is called adenocarcinoma, which starts from one of the common cell types found in the lining of the stomach. There are several types of adenocarcinoma. Because other types of gastric cancer occur much less frequently, this article focuses on adenocarcinoma of the stomach.

Adenocarcinoma of the stomach is a common cancer of the digestive tract worldwide, although it is relatively uncommon in the United States. It occurs most frequently in men over 40 years old. This form of gastric cancer is extremely common in Japan, Chile, and Iceland. The rate of most types of gastric adenocarcinoma in the United States has declined over the years. Experts think the decrease may be related to reduced intake of salted, cured, and smoked foods. Gastric adenocarcinoma occurs most frequently in men over age 40.

Diagnosis is often delayed because symptoms may not occur in the early stages of the disease, or because patients self-treat symptoms that may be common to other, less serious gastrointestinal disorders (bloating, gas, heartburn, and a sense of fullness).

Risk factors associated with gastric cancer are a family history of gastric cancer, Helicobacter pylori infection, blood type A, smoking, a history of pernicious anemia, a history of chronic atrophic gastritis, and a prior history of an adenomatous gastric polyp larger than 2 centimeters.