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Helicobacter pylori infection and gastric cancer

© David Olle

Helicobacter pylori Infection

The medical community currently believes that the majority of stomach ulcers are due to infection with the bacterium Helicobacter pylori, rather than excessive acid secretion. The organism lives under the mucus layer lining the stomach, but does not actually invade the mucosa. In this manner, the organism protects itself from acid and pepsin secretions of the stomach. H. pylori further protects itself by secreting urease, an enzyme that breaks down urea into ammonia and carbon dioxide, the ammonia in turn neutralizing stomach acid. The activities of the organism cause a thinning and breakdown of the mucosal layer. The stomach lining is now exposed to acid and pepsin, and ulcers may develop. In these cases, stomach acid is a contributing factor, but not a cause of the ulcers.

Does H. pylori infection cause stomach cancer?

H. pylori causes a chronic inflammation in the stomach lining. The question arises whether this inflammation can lead to progressive changes in the mucosal cells leading to cancer. Hansson and co-workers 3 found that H. pylori infection is an independent risk factor for gastric adenocarcinoma. A much larger EUROGAST study 2 involved 17 populations from 13 countries. The results indicated that H. pylori infection caused a six-fold increased risk in gastric cancer. As the chronic infection continues, it progresses to atrophic gastritis. A recent study 4 found that H. pylori infection promotes this progression leading to stomach cancer. The authors also found that it was quite rare for any type of gastric cancer to develop in an H. pylori-free healthy stomach.

H. pylori infection and esophageal cancer

A study reported at the 2003 Digestive Diseases Week scientific meeting found that individuals infected with H. pylori had a 72% lower risk of developing esophageal cancer than uninfected individuals. Stomach contents enter the esophagus through the process of acid reflux due to the relaxation of the lower esophageal sphincter. Contrary to the stomach, the esophagus does not have protective mucus covering its mucosal lining. This lack of protection makes the esophageal lining more susceptible to the effects of stomach acid. Since H. pylori infection reduces stomach acid secretion, the authors theorize that the esophagus is exposed to less stomach acid and subsequent progressive changes leading to cancer.

Treatment of H. pylori infection

Since H. pylori infection increases the risk of gastric cancer, but may reduce the risk of esophageal cancer, the physician is put in a quandary. However gastric ulcers must be treated, and the incidence of esophageal cancer is much lower than gastric cancer. To treat ulcers due to H. pylori infection, the organism must first be eradicated, followed by treatment of the ulcers so that the healing process can begin. The infection can be treated with antibiotics, but H. pylori can rapidly develop resistance to common antibiotics. Currently, a combination of drugs is used, since the use of individual drugs is ineffective. 5

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