Colorectal cancer risk linked to stomach bacterium, inflammation

Common ulcer-causing infection more frequent in people with polyps

WASHINGTON — A chronic stomach infection or high levels of inflammation may place a person at risk of colon cancer — or serve as an early warning sign of the disease — according to two studies presented April 19 at a meeting of the American Association for Cancer Research.

Past research has shown that chronic infections or persistent inflammation increase cancer risk in the lungs, liver and other tissues, said William Nelson, a medical oncologist at Johns Hopkins Medical Institutions, in Baltimore, who didn’t participate in either study. “It’s a growing trend,” he said. The new studies offer evidence “that colon cancer is the next one knocking on the door,” Nelson said.

In a study conducted at Howard University in Washington, D.C., gastroenterologist Duane Smoot and his colleagues analyzed the medical records of 1,262 blacks over age 40 who had undergone a colonoscopy to check for polyps in the colon and also had an endoscopy to assess stomach health. The endoscopies revealed that about one-third of the patients had a stomach infection of Helicobacter pylori , a common bacterium known to cause low-grade inflammation, ulcers and possibly even stomach cancer. The researchers found that 43 percent of patients in the study who harbored H. pylori also had colorectal polyps, compared with 34 percent of those not infected with H. pylori . Polyps can be precancerous and are routinely removed during colonoscopy. H. pylori infection increases the body’s manufacture of a hormone called gastrin, which can have a pro-growth effect on cells that, if unchecked, could lead to cancerous growth, Smoot said. He speculated that H. pylori infection may also trigger production of inflammation-causing cells that produce free radicals, unstable reactive oxygen species that can cause cancer-inducing mutations. Researchers should test for the presence of H. pylori in the colon and specifically in polyps, he said, to clarify the microbe’s role in colon cancer. In the other study, researchers at Vanderbilt University in Nashville and the Shanghai Research Institute compared blood levels of C-reactive protein in 209 Chinese women who had colon cancer and 279 women without it who matched the cancer patients in other respects. CRP is a marker of inflammation in the body. When researchers ranked CRP levels for all the women, those with levels in the highest one-fourth were more than twice as likely to have colon cancer as were those with CRP levels that ranked in the lowest one-fourth. Even if CRP levels and cancer are associated, this study doesn’t establish a cause-and-effect relationship, said study coauthor Gong Yang, a physician and epidemiologist at Vanderbilt. In the study, women with more advanced colon cancer had higher CRP levels, he noted, which suggests that the cancer itself might be spurring this inflammatory protein. High CRP levels might therefore be a warning sign of early colon cancer in some people, he added. Many common cancers arise in cells that line the insides of organs, such the lung and colon, Nelson said. “This is the barrier from the outside world, and these areas carry huge amounts of bacterial flora. So these are sites in which the immune inflammatory response is going to try to control that flora — and there is always going to be collateral damage.” If that damage includes changes to the cells’ genes and disturbs their growth cycle, such cells can turn malignant, he said. Nearly 150,000 people in the United States are diagnosed with colorectal cancer each year and about 50,000 die from the disease, according to the American Cancer Society.

More Stories from Science News on Health & Medicine