H. Pylori Has Mixed Role in Cancer
Ulcer Bacterium Raises Risk of Some Stomach Cancers, Lowers Others
Oct. 17, 2006 -- A bacterium that causes ulcers also increases the risk of cancer of the lower stomach, but it seems to protect against cancer of the upper stomach that includes the junction of the esophagus, researchers from the National Cancer Institute report.
The seemingly paradoxical findings may help explain the changing incidence of these cancers in the industrialized world.
bacterial infection has been on the decline in the United States and other industrialized countries over the past decades, due to improved sanitation and the introduction of antibiotic drugs.
This decline has been accompanied by a dramatic drop in lower stomach cancers and, more recently, an equally dramatic rise in cancers of the junction between the lower esophagus and upper stomach.
"These cancers were basically nonexistent in the U.S. 30 years ago," NCI researcher Farin Kamangar, MD, PhD, tells WebMD. "During the past 20 years or so there has been a 350% increase in the rates of these cancers among white males in this country."
Threefold Lower Risk
In an effort to better understand the role of H. pylori in stomach cancerstomach cancer, Kamangar and colleagues recruited 468 Finnish people participating in a larger cancer prevention trial and tested their blood for evidence of the gut bacteria. Half of the 468 had stomach cancer, and half did not. The patients were recruited for the trial between the mid- to late-1980s.
As expected, those who tested positive for H. pylori had a higher risk of developing cancer of the lower stomach. Their risk was found to be almost eight times higher than study participants with no history of H. pylori infection.
Somewhat more surprising, the risk of developing cancer of the upper stomach including the junction to the esophagus was three times lower among participants who tested positive for H. pylori infection.
The findings are published in the October issue of the Journal of the National Cancer Institute.
One theory is that H. pylori infection helps protect against junctional cancer by reducing the esophagus' exposure to stomach acid, Kamangar says.
involves the backup of stomach acid into the esophagus. Chronic acid reflux can cause a condition called Barrett's esophagus, which is a risk factor for esophageal cancer.