A large meta-analysis published in Frontiers, "Risk of Colorectal Cancer in Patients With Irritable Bowel Syndrome: A Meta-Analysis of Population-Based Observational Studies," that included over one million participants, found that people who were newly diagnosed with irritable bowel syndrome (IBS) had a significantly higher chance of being diagnosed with colorectal cancer within the first year after their IBS diagnosis. The study showed the risk was nearly six times higher during that initial year compared to people without IBS.

However, after a year, the research concluded that the risk of colorectal cancer dropped to levels similar to the general population. This suggests that IBS itself does not cause colon cancer, rather some early cases of colon cancer may be mistakenly diagnosed as IBS, because the symptoms overlap.

Key differences emerge as the disease progresses. The symptoms of colon cancer tend to worsen and persist, whereas in IBS, symptoms often come and go in cycles and may get better following a bowel movement or through dietary modifications and stress management. More often, colon cancer presents with warning signs that are not seen in IBS, including rectal bleeding or bloody stools-potentially bright red or dark and tarry in appearance-unexplained weight loss, fatigue, anemia because of bleeding, narrowing of the stool, and feelings of fullness or obstruction. Symptoms of IBS, like bloating or crampy pain typically do not involve bleeding or systemic findings such as weight loss.

Pain characteristics can also vary: IBS abdominal pain is often cramp-like, generalized, and relieved by passing gas or stool, whereas colon cancer pain is usually persistent, localized, and not relieved by bowel movements. The symptoms of IBS also frequently have triggers, such as stress or a particular food intake, which do not influence the symptoms of colon cancer.

Overlapping symptoms make the distinction of early colon cancer from IBS elusive and require great caution in medical evaluation. Symptoms that persist or are worsening, such as blood in the stool or systemic signs like unexplained weight loss and fatigue, call for diagnostic testing like a colonoscopy to rule out cancer. Colonoscopy is considered the gold standard because it allows direct visualization and biopsy of any suspicious lesions.