Bowel cancer and how serrated polyps affect risk

Serrated polyps were once thought harmless but now have healthcare providers on alert. New research suggests that people with these polyps should be examined more often for bowel cancer.

A small sessile serrated lesion.

From left: A small sessile serrated lesion, which can be fairly subtle and difficult to detect. A serrated polyp injected with blue dye makes it easier to spot. A serrated polyp being resected by a snare.

Bowel cancer, also known as colon cancer and colorectal cancer, often begins with small polyps that are not cancerous and cause no symptoms. However, these polyps can gradually become cancerous. Through bowel cancer screening, your health care provider can detect and remove polyps while they are still harmless.

"Our view of serrated polyps has come a long way in the last two decades, moving from seeing them as benign lesions that do not develop into cancer, to recognizing them as lesions that may account for up to one-third of all colorectal cancers," James East, M.D., a gastroenterologist at Mayo Clinic Healthcare, in London, writes in a commentary in the journal Gut.

Until recently, there wasn't enough data on serrated polyps to justify closer surveillance for bowel cancer. The sawtooth-edged, flat growths in the bowel are nearly clear and can be difficult to detect during colonoscopies. However, a large new study published in Gut by Dan Li, M.D., and colleagues at Kaiser Permanente now suggests that people with serrated polyps alone or along with another type of polyp (adenomas) may need more frequent screening, Dr. East says.

Experts have long understood that adenomas were precursors to cancer. But the Kaiser Permanente study shows that serrated polyps alone may increase cancer risk by about the same amount. The presence of both kinds of polyps raises risk still even more, Dr. East notes. However, more research is needed to better understand how these types of polyps affect cancer risk, Dr. East says.

It’s possible that measuring risk by the type of polyp isn't the most effective approach. Other markers may be more accurate, such as comparing the number of polyps to other bowel cancer risk factors, including a high-fat diet, obesity, smoking, heavy alcohol use or inflammatory intestinal diseases such as Crohn's disease and ulcerative colitis, he adds.