Scientists Find Worrying Link Between Common Ulcer Germ and Colorectal Cancer

A common bacterial infection might be more dangerous than we thought after new research shows Helicobacter pylori, a leading cause of ulcers and stomach cancers, possibly fueling a sizable percentage of colorectal cancer cases. Scientists in Hong Kong estimated the potential global burden of colorectal cancer cases linked to H. pylori infection based on dozens of earlier studies. They found evidence that people with these infections are noticeably more likely to develop colorectal cancer, and that roughly one in every five of these cancers worldwide might be linked to the common stomach germ. Though more research is needed to untangle this connection, screening and treatment programs for H. pylori could make a substantial dent in the incidence of colorectal cancer, the researchers say. “These findings may inform primary [colorectal cancer] prevention strategies, particularly in regions with high H. pylori prevalence and limited resources,” the authors wrote in their paper, published last month in the journal eGastroenterology. A cancer burden H. pylori loves to call the human stomach home, and more than half of the world has had an infection of it at some point in their lives. Though it can cause miserable gastrointestinal infections, most people carrying it never show signs of acute illness. Chronic infections of H. pylori, however, can eventually cause ulcers that inflame and wear away the lining of the stomach. Scientists have long known that chronic H. pylori and its accompanying ulcers can increase people’s risk of stomach cancer. The World Health Organization even lists the bacteria as one of 13 major infections that are carcinogenic. Some research has also suggested that H. pylori can raise the risk of colorectal cancer, though we’re less certain about how many of these cases it might be involved in. To get a better sense of this burden, the researchers examined 43 studies across the world that collectively involved 48.7 million people. Some of these studies attempted to track how common H. pylori infections were in a given population, while others tried to figure out the exact added risk of colorectal posed by having these infections. Overall, the researchers found that having a H. pylori infection was associated with a 59% higher risk of developing colorectal cancer. Globally, they estimated that 22% of all colorectal cancers may potentially be related to H. pylori exposure. What does this mean for cancer prevention? These are ultimately only estimates, and the numbers vary depending on the data being analyzed. When the researchers looked at a more narrow selection of studies, for instance, the attributable burden of H. pylori dropped to 12% of all colorectal cases. Cancer is also complicated and often caused by multiple factors. Notably, the risk of these infections causing colorectal cancer seemed to differ between countries. That said, chronic H. pylori infections can be detected relatively easily and then treated with antibiotics. And research has shown that screening and treatment programs for H. pylori in high-risk areas of the world can prevent new cases of stomach cancer down the road, though these programs have still been limited in scope so far. The researchers are careful to note that “high-quality, prospective studies with long-term follow-up” are needed to know whether these programs can also reduce the risk of colorectal cancer. But given these findings, such initiatives may be even more helpful than we expected.