Does IBS elevate long-term risk of cancer?

People with irritable bowel syndrome (IBS) are not at increased overall risk of cancer relative to the general population, reveals a study. On the contrary, those with IBS appear to have a lower risk of incident colorectal cancer (CRC) and cancer-specific mortality.

“[O]ur findings provide reassurance for patients with IBS that IBS itself unlikely develops into CRC eventually and will not shorten life span owing to cancer,” said the researchers, led by Shanshan Wu, PhD, Department of Gastroenterology, Beijing Friendship Hospital, Capital Medical University in China.

“Both clinicians and patients with IBS should take this into consideration for better management of IBS conditions and save healthcare resources,” they added.

Wu and colleagues examined participants free of inflammatory bowel disease, celiac disease, and any cancer at baseline from the UK Biobank, with IBS patients as the exposure group and non-IBS patients as the reference group. They investigated the associated risk of incident malignancies and related mortality using the Cox proportional hazard model.

A total of 449,595 participants were included, of which 22,338 (5.0 percent) were diagnosed with IBS. Nearly 3,000 cases of incident cancer were identified in IBS patients (11.47 per 1,000 person-years), compared with 60,556 cases in reference individuals (12.51 per 1,000 person-years), during a median follow-up of 12.2 years. Of the cases, 512 and 12,282 cancer-specific deaths occurred in IBS and non-IBS groups, respectively. [Am J Gastroenterol 2022;117:785-793]

The adjusted hazard ratios (HR) were 0.97 (95 percent confidence interval [CI], 0.93‒1.00; p=0.062) for overall cancer mortality and 0.83 (95 percent CI, 0.76‒0.91; p<0.001) for cancer-specific mortality among IBS patients compared with non-IBS participants. The risk of digestive cancers (HR, 0.79, 95 percent CI, 0.71‒0.89), particularly colon (HR, 0.75, 95 percent CI, 0.62‒0.90) and rectal (HR, 0.68, 95 percent CI, 0.49‒0.93), was reduced in patients with IBS.

These results were consistent in sensitivity and subgroup analyses by age and sex.

“Our study suggests that long-term CRC risk in IBS is 27-percent lower than general population after adjusting multiple confounders,” the researchers said. A possible explanation for this was the greater extent of medical examinations, specifically a higher frequency of colonoscopy or sigmoidoscopy, in IBS patients relative to reference individuals.

“Thus, the increased surveillance may lead to increased likelihood of earlier detection of colorectal precancerous lesion, adenoma and polyps, and further earlier treatment, which could thereby [lower the] risk of developing CRC in patients with IBS,” they added.

Cancer of the central nervous system

Additionally, this study showed that the HR of IBS associated with central nervous system (CNS) cancer was 1.14 (95 percent CI, 0.83‒1.57), which was even higher in females (HR, 1.21, 95 percent CI, 0.81‒1.80) compared with non-IBS individuals.

“Because IBS is considered as a disorder of gut-brain interaction, it has been proved that patients with IBS experience altered CNS processing in sensory, emotional, arousal, and prefrontal cortical regions of the brain,” the researchers said. [Lancet 2020;396:1675-1688]

CNS cancer risk could be higher in IBS patients because of the long-lasting and recurrent gut-brain interaction, they added.

“However, because of the limited number of incident CNS cancers, our results were with wide CI and statistical power was insufficient (power=12.59 percent). Hence, the follow-up with a larger sample size of CNS cancer is necessary to rule out increased risk in patients with IBS,” the researchers said.