Irritable Bowel Syndrome (IBS) and Colorectal Cancer: What is the Connection?

Inflammatory bowel disease (IBD) is known to raise the risk of developing colorectal cancer. How much? It depends on how much of your colon and rectum is affected by IBD. Having IBD does not mean that you will develop colorectal cancer, and risk is changing over time as new treatments are available to control IBD. 

Nonetheless, the connection is well-established and should inform screening procedures and discussions with a health care professional and/or gastroenterologist. 

What is inflammatory bowel disease? 

Inflammatory bowel disease is characterized by long-standing, or chronic, inflammation in the digestive tract. There are two types of IBD:  

• Ulcerative colitis, which typically affects the lining of the large intestine, or colon, and the rectum.  
• Crohn’s disease, which can affect the lining of the colon, rectum, and other parts of the digestive tract and may involve deeper layers of the membrane. 

Symptoms vary but can include diarrhea, fatigue, abdominal pain and cramping, and blood in the stool. People experiencing these symptoms should seek the opinion of a healthcare professional. 

Why does IBD raise colorectal cancer risk? 

It’s believed that inflammation caused by Crohn’s disease and ulcerative colitis leads to a high turnover of cells lining the intestines. This rapid rate of cell replacement means there is a higher chance of a mutation occurring, which could develop into cancer.  

This means that the risk of colorectal cancer rises as the duration of inflammatory bowel disease increases.  

How can you manage cancer risk with IBD? 

A person with IBD should consult regularly with a gastroenterologist to treat IBD symptoms and begin an appropriate cancer screening regimen.  

There isn’t a cure for ulcerative colitis or Crohn’s disease. Instead, treatments for IBD target the inflammation that may be at the root of a cancer’s development. “We think lowering inflammation can also lower cancer risk,” says Jeffrey Meyerhardt, MD, MPH, a Dana-Farber medical oncologist who co-directs the Colon and Rectal Cancer Center. “Some of the drugs themselves may also lower cancer risk.”  

Conversely, some of the immunosuppressive drugs used to treat Crohn’s slightly increase the risk of developing lymphoma. Weighing these risks is complicated and requires the opinion of a healthcare provider. 

Managing inflammation is also important in enabling physicians to properly screen for cancer and identify areas of dysplasia. Exercising regularly and sticking to a healthy diet can also improve IBD symptoms. 

Does IBD change colorectal cancer screening recommendations? 

Regular screening for colorectal cancer is crucial for patients with Crohn’s disease or ulcerative colitis.  

Typically, colorectal cancer presents as polyps (growths in the intestine) which can be identified with a colonoscopy alone. Colorectal cancers which arise in the setting of IBD present themselves differently. They often begin as dysplasia (abnormal cells within the tissue).  

“Unlike polyps, dysplasia are flat lesions, making them more difficult to detect,” Meyerhardt says. So, gastroenterologists will typically recommend taking a random sample of biopsies along sections of the bowels during the colonoscopy. 

Comprehensive screening can lead to cancer being diagnosed at an earlier stage before it has spread, improving treatment outcomes. “Screening recommendations will vary from person to person,” Meyerhardt says. “They will depend on the severity of the disease and the disease’s duration. This why it’s crucial to get a gastroenterologist involved in the discussion early.” 

Does IBD affect cancer treatment? 

“When a patient with inflammatory bowel disease comes to us, we consider the elevated risk for recurrence and the development of other cancers,” Meyerhardt explains. “So, we may recommend a more extensive surgery that will help to combat that risk.” 

Chemotherapy guidelines are similar for patients with and without IBD, but the drugs may be more difficult to tolerate for patients with IBD. To ensure tolerance, oncologists like Meyerhardt may make minor adjustments to the treatment regimen. 

In Dana-Farber’s Colon and Rectal Cancer Center, patients receive comprehensive care from a multi-disciplinary group of experts who specialize in cancer. This way cancer and any comorbidity, like inflammatory bowel disease, can be managed in tandem. 

About the Medical Reviewer

Dr. Meyerhardt received his MD from Yale School of Medicine in 1997. He completed a residency in internal medicine at Beth Israel Deaconness Medical Center, in Boston, followed by a medical oncology fellowship at DFCI. He joined the Gastrointestinal Cancer Center at DFCI in 2002..