Irritable Bowel Syndrome and Colorectal Cancer

Irritable bowel syndrome (IBS) is a gastrointestinal (GI) disorder that presents with a constellation of both GI and non-GI symptoms, and which has become the most commonly diagnosed GI disorder. Although the number of patients diagnosed with IBS is increasing, it is still a new GI diagnosis with limited data on its associated risk for cancer. As more patients continue to be diagnosed with IBS, cancer risk will undoubtedly become one of the more crucial topics researched and discussed with patients.

Patients with IBS present with a multitude of symptoms, most of which are typically nonspecific. This can often complicate the differential diagnosis, as many GI malignancies, especially colorectal cancer (CRC), will present with similar symptoms. Some of the most common presenting GI symptoms include chronic, nonlocalized abdominal pain and cramping, frequent alterations in bowel movements (ranging from constipation to diarrhea), excessive bloating or flatulence, and mucus-containing stools. In addition to their GI symptoms, patients with IBS can also present with general malaise, weight loss, and chronic pain (as seen with fibromyalgia). In attempts to standardize how to diagnose IBS, the Manning and Rome criteria were developed.¹ The Rome III criteria are the most recently updated guidelines and require recurrent abdominal pain or discomfort for at least 3 days per month in the last 3 months, associated with at least two of the following three symptoms: improvement with defecation, onset associated with a change in frequency of stool, and onset associated with a change in form or appearance of stool.¹

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Depending on the criteria used to diagnose IBS and the country in which the disease originated, the prevalence of IBS is reported to be between 5% and 25% of the population.^2,3 When evaluating a patient who may have IBS, it is vital to conduct a thorough history and physical. Patients who present with alarming symptoms such as severe abdominal pain, melena, bright red blood per rectum, weight loss, gross laboratory abnormalities, or a strong family history of GI malignancies or inflammatory bowel disease (IBD) should always have life-threatening conditions ruled out initially while still including IBS on the differential diagnosis.

The exact pathophysiology underlying IBS is not fully understood; however, increased inflammation and immune system activation have both been proposed. If the GI tract of the patient with IBS does support a hyper-inflammatory and altered immune environment, then the hypothetical risk for developing cancer is possible. Most of the clinical studies evaluating the risk of cancer in patients with IBS have focused on CRC. Norgaard et al³ conducted a retrospective review of over 57,000 patients with IBS in Denmark that showed a 5- to 8-fold increased risk of rectal and colon cancer, respectively, within the first 3 months of a formal IBS diagnosis. However, in years 1 through 10 after diagnosis, the authors did not find an increased risk of CRC. A similar study was performed by Hsiao et al⁴ in Taiwan, which retrospectively evaluated over 91,000 patients. There was an increased incidence and risk of CRC within the first 2 years of IBS diagnosis, but there was no increased risk after 2 years of diagnosis. As just mentioned, there is some overlap in symptoms experienced by patients with IBS and CRC, which may explain the disparity in increased CRC risk soon after the IBS diagnosis, which does eventually disappear.

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Both of these studies were both somewhat limited based on their retrospective design as well as the evaluation of a patient population within a limited demographic region. The link between IBS and CRC has not been fully evaluated and additional clinical studies are needed to further clarify the association or lack thereof. However, at least preliminarily, it does not appear that there is an increased risk of CRC in patients with IBS.

References

1. Longstreth GF, Thompson WG, Chey WD, et al. Functional bowel disorders. Gastroenterology. 2006;130(5):1480-1491.
2. Hungin AP, Whorwell PJ, Tack J, Mearin F. The prevalence, patterns and impact of irritable bowel syndrome: an international survey of 40,000 subjects. Aliment Pharmacol Ther. 2003;17(5):643-650.
3. Nørgaard M, Farkas DK, Pedersen L, et al. Irritable bowel syndrome and risk of colorectal cancer: a Danish nationwide cohort study. Br J Cancer. 2011;104(7):1202-1206.
4. Hsiao CW, Huang WY, Ke TW, et al. Association between irritable bowel syndrome and colorectal cancer: a nationwide population-based study. Eur J Intern Med. 2014;25(1):82-86.