Gene May Explain Why Some Have Higher Stomach Cancer Risk
March 22, 2000 (Ithaca, N.Y.) -- People who become infected with the bacterium Helicobactor pylori are at higher risk for either ulcers or stomach cancer -- but not both, according to a study in this week's issue of Nature. Emad M. El-Omar, MD, and researchers at the National Cancer Institute have identified a gene that partly accounts for this either/or situation.
El-Omar tells WebMD that people who are infected with the bacterium and who also have this gene produce large amounts of an immune signal called "interleukin-1-beta." This causes inflammation in the stomach and reduces the amount of acid that the stomach secretes. People with the H. pylori bacterium who do not have this gene have less inflammation and are more able to fight off the infection. They also have higher levels of gastric acid, which promotes digestion and help cleanse the stomach of harmful substances.
Although stomach acid is often blamed for indigestion, El-Omar says that it is actually a good thing: "Gastric acid is the stomach's first line of defense."
People who have the "low acid" gene are less able to fight off H. pylori and other infections. The result is that inflammation can spread throughout the stomach and eventually damage the cells that produce stomach acid. This decreases the stomach's ability to defend itself against toxins that can cause cancer, El-Omar says.
El-Omar found that normally occurring variations in the gene explain whether a person will develop ulcers or cancer -- or nothing -- in response to an H. pylori infection.
"If you have a duodenal ulcer, it is your insurance policy against gastric cancer," El-Omar tells WebMD. "We wondered why that is. One clue was that when gastric acid secretion is inhibited for a long time in the presence of H. pylori, there can be a shift in the pattern of gastric inflammation from the ulcer type (which occurs in the lower part of the stomach) to the cancer-associated type (in the upper part). We suspected that genetic factors might partly explain the difference."
The researchers calculate that the "high risk" gene may be responsible for 38% of stomach cancers. Stomach cancer is the second most common form of cancer worldwide, and people who have H. pylori in their stomachs are three to six times more likely to develop it than those who don't. About half the world's population carries the bacterium.