H. pylori is thought to spread through contaminated food and water and through direct mouth-to-mouth contact. In most populations, the bacterium is first acquired during childhood. Infection is more likely in children living in poverty, in crowded conditions, and in areas with poor sanitation.
What is gastric cancer?
Gastric cancer, or cancer of the stomach, was once considered a single entity. Now, scientists divide this cancer into two main classes: gastric cardia cancer (cancer of the top inch of the stomach, where it meets the esophagus) and non-cardia gastric cancer (cancer in all other areas of the stomach).
According to NCI’s Surveillance, Epidemiology, and End Results (SEER) Program, an estimated 21,600 people in the United States will be diagnosed with gastric cancer and 10,990 people will die of this cancer during 2013. Gastric cancer is the second most common cause of cancer-related deaths in the world, killing approximately 738,000 people in 2008 (3). Gastric cancer is less common in the United States and other Western countries than in countries in Asia and South America.
Overall gastric cancer incidence is decreasing. However, this decline is mainly in the rates of non-cardia gastric cancer (4). Gastric cardia cancer, which was once very uncommon, has risen in incidence in recent decades (5).
Infection with H. pylori is the primary identified cause of gastric cancer. Other risk factors for gastric cancer include chronic gastritis; older age; male sex; a diet high in salted, smoked, or poorly preserved foods and low in fruits and vegetables; tobacco smoking; pernicious anemia; a history of stomach surgery for benign conditions; and a family history of stomach cancer (6, 7).
H. pylori has different associations with the two main classes of gastric cancer. Whereas people infected with H. pylori have an increased risk of non-cardia gastric cancer, their risk of gastric cardia cancer is not increased and may even be decreased.
What evidence shows that H. pylori infection causes non-cardia gastric cancer?
Epidemiologic studies have shown that individuals infected with H. pylori have an increased risk of gastric adenocarcinoma (1,2,8