Exposure to the stomach microbe Helicobacter pylori may be associated with more than 1 in 5 cases of bowel cancer worldwide, suggests an exploratory risk attribution study, published in the open access journal eGastroenterology.
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, conclude the researchers.
Bowel cancer is the second leading cause of cancer related death: in 2022, there were nearly 2 million new cases and 900,000 deaths from the disease worldwide, note 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, they explain.
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%).
When stratified by region and country, the Western Pacific and Mongolia had the highest estimated proportions of cases potentially linked to H pylori exposure–25% and 36%, respectively—while China had the highest absolute number of cases linked to exposure:139, 619.
This contrasts with similarly high H pylori prevalence in Africa, South-East Asia, and the Eastern Mediterranean, but comparatively lower estimated proportions of cases attributable to H pylori exposure.
Exploratory data pattern analysis suggested that the proportion of bowel cancers linked to exposure was greater among those born in more recent decades (1960s and 1970s), rising from 9.5% in those born before 1947 to around 10% among those born in 1948–62, and 15% among those born in 1963–77.
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," highlight the researchers.
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.
