Scientists at the Fred Hutchinson Cancer Research Center report that they have found a specific strain of Helicobacter pylori strongly correlated with stomach cancer. They say their study (“Increased H. pylori stool shedding and EPIYA-D cagA alleles are associated with gastric cancer in an East Asian hospital”), published in PLOS ONE, could eventually be used to shape therapeutic and screening strategies for patients.
“Helicobacter pylori infection increases risk for gastric cancer. Geographic variation in gastric cancer risk has been attributed to variation in carriage and type of the H. pylori oncogene cagA. Colonization density may also influence disease and cagA has been associated with higher shedding in stool. However, the relationship between H. pylori load in the stool and in the stomach is not clear,” write the investigators.
“To investigate possible differences in H. pylori load in the stomach and shedding in stool, H. pylori load and cagA genotype were assessed using droplet digital PCR assays on gastric mucosa and stool samples from 49 urea breath test–positive individuals, including 25 gastric cancer and 24 noncancer subjects at Henan Cancer Hospital, Henan, China.
“Quantitation of H. pylori DNA indicated similar gastric loads among cancer and noncancer cases, but the gastric cancer group had a median H. pylori load in the stool that was six times higher than that of the noncancer subjects. While the cagA gene was uniformly present among study subjects, only 70% had the East Asian cagA allele, which was significantly associated with gastric cancer (Fisher’s Exact Test, p = 0.03).
“H. pylori persists in a subset of gastric cancer cases and thus may contribute to cancer progression. In this East Asian population with a high prevalence of the cagA gene, the East Asian allele could still provide a marker for gastric cancer risk.”
Collaborating with researchers at Zhengzhou University, the Fred Hutch team ran tests on 49 patients' stomach endoscopy and stool samples, looking for H. pylori with a variant of the cagA gene, known as EPIYA D. They found 91% of the patients with the EPIYA D strain also had cancer.
“We've known the H. pylori bacterium has a strong correlation to stomach cancer, but it's been difficult to pinpoint why certain patients, especially in areas like Northeast Asia, are more susceptible to stomach cancer,” says Nina Salama, Ph.D., senior author of the study and a member of Fred Hutch's Human Biology and Public Health Sciences divisions. “While it's preliminary in nature, these results could be the first step towards identifying the highest risk groups and improving screening and treatment plans.
“Unfortunately, infections like H. pylori directly or indirectly, cause up to 20% of cancers worldwide. But knowing the cause gives us a clear target to develop vaccines for prevention or tools to better recognize risk.”