The bacteria Helicobacter pylori substantially increase the risk of cancer in the lower stomach, but it may decrease the risk of cancer near the junction between the esophagus and the stomach, according to a study in the October 19 Journal of the National Cancer Institute.
This finding may help explain the changing rates and distributions of these cancers in Western countries over the past century.
Infection with H. pylori, which is known to cause ulcers, has also been associated with certain types of gastric cancer, but the strength of association varies with where the cancer is located in the stomach. Two types of gastric cancer commonly exist -- cardia, or cancer of the upper stomach joining the esophagus; and noncardia, or cancer of the lower stomach.
A group of researchers led by Farin Kamangar, M.D., Ph.D., of the National Cancer Institute in Bethesda, Md., selected 234 cardia and noncardia gastric cancer patients in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study and matched them to controls. They assessed all of the subjects for H. pylori infection by testing their blood for antibodies that indicate prior infection.
The authors found that the subjects infected with H. pylori had a higher risk of developing noncardia gastric cancer and a lower risk of developing cardia gastric cancer. They suggest that a decrease in H. pylori infections during the past century may be one reason that scientists have observed increasing rates of cardia and decreasing rates of noncardia gastric cancers in Western countries.
"The results of this study suggest that caution may be warranted against mass treatment to eradicate H. pylori ," the authors write.
In an accompanying editorial, Olof Nyren, M.D., Ph.D., of the Karolinska Institute in Sweden, and William J. Blot, Ph.D., of the International Epidemiology Institute in Rockville, Md., write, "It seems prudent to include the putative protective effect of H. pylori against adenocarcinoma of the esophagus or cardia in the equation when drawing up prevention plans for gastric cancer."