A bacterium best known for causing stomach ulcers may also be playing a significant role in bowel cancer, according to new research that raises fresh questions about the disease’s origins.
A carcinogen with wider reach
The study, published in the open access journal eGastroenterology, found that exposure to Helicobacter pylori “may be associated with more than 1 in 5 cases of bowel cancer worldwide”.
Those born in more recent decades may be more at risk of the disease after exposure, the analysis suggests, and high-quality long-term studies are needed to determine if eradication therapy with antibiotics significantly lowers bowel cancer risk, according to the researchers.
“H pylori is categorised as a group 1 (definite) human carcinogen given its established causal association with stomach cancer. But its potential role in bowel cancer risk remains hotly debated, despite accumulating evidence,” explain the researchers.
The study
In a bid to strengthen the evidence base and inform future preventive strategies in countries with a high prevalence of H pylori infection and limited resources, the researchers set out to estimate the extent to which exposure might be related to the global toll of bowel cancer cases.
They therefore drew on data from systematic reviews and pooled data analyses, stratified by various factors, including region, diagnostic method, sex, access to a national bowel cancer screening programme, and the use of eradication therapy.
They derived international estimates of bowel cancer cases from the Global Cancer Observatory (GLOBOCAN) for 2022.
Their analysis revealed that exposure to H pylori was associated with a 1.6-fold greater risk of bowel cancer than no exposure.
No statistically significant differences were observed when categorised by sex, age (above and below 60), diagnostic method, or the presence of a national bowel cancer screening programme.
In the 4 observational studies that reported on this, H pylori eradication therapy was associated with a reduced risk of the disease, but only after 10 years.
Globally, pooled risk estimates from 43 studies (48, 694,403 people) indicated that H pylori exposure might be linked to around 1 in 5 (22%) of bowel cancer cases.
The estimated proportion attributable to exposure was much lower, however, when restricted to 14 population-based and cohort studies (12%).
Other influential risk factors
The researchers point out that there are many potentially influential risk factors in the development of bowel cancer, which include non-modifiable ones, such as genetics and age, as well as modifiable ones, such as those related to lifestyle and diet.
And, worldwide, these account for a larger estimated proportion of bowel cancer cases than H pylori, they add.
“Population-level H pylori control may help prevent gastric cancer and, if the link with [bowel cancer] is causal, could reduce [this] burden in high-prevalence areas. However, success depends on local epidemiology, healthcare capacity, and integration with existing [bowel cancer] screening.
“As with primary gastric cancer prevention, large-scale H pylori eradication raises concerns about antibiotic stewardship and resistance, and treatment side effects,” the researchers highlight.
The findings underscore the importance of well-designed randomised clinical trials and other prospective investigations evaluating the impact of H pylori and its eradication on [bowel cancer] risk, as well as potential modifying factors, they conclude.
Bowel cancer stats
Bowel cancer is already the second leading cause of cancer death globally, with close to 2 million new cases and 900,000 deaths recorded in 2022 alone.
