SALT LAKE CITY — Not all colon cancers are recognized immediately following a colonoscopy, according to new research from the Huntsman Cancer Institute.
A Utah population-based study reveals that about 6 percent of colorectal cancers are diagnosed within three to five years after a patient gets a clean colonoscopy report.
The cancers are overlooked at the time of the colonoscopy or develop rapidly before the next colonoscopy is ordered, classifying them as "missed" cancer diagnoses, according to the research published online Thursday in the academic journal Gastroenterology.
"Not only did we find that colonoscopy isn't perfect, we discovered a number of factors associated with these 'missed' cancers," said Dr. N. Jewel Samadder, lead author of the study and an investigator at Huntsman. He said the condition, involving possibly flatter and faster growing polyps, arises most in patients over age 65, patients with a family history of colorectal cancer and patients in whom polyps were previously found.
The missed cancers were also more likely to appear in the right side of the colon, at the far end of the colonoscope's reach.
"Our first thought was that perhaps doctors did not view the entire colon, or that preparation for the procedure was not complete, which would obscure their view," Samadder said. "However, the medical records of the patients with missed cancers showed these problems were seldom present."
The study included results from colonoscopies performed at University of Utah Health Care and Intermountain Healthcare facilities between 1995 and 2009, as well as data from the Utah Population Database, which combines genealogical, medical and demographic data with cancer records from the Utah Cancer Registry.
The discovery enhances the importance of doctors obtaining a complete medical history, accounting for older age, family history of colorectal cancer and prior history of polyps, so that more time can be spent examining patients with increased risk factors, said Samadder.
The American College of Gastroenterology, among others, recommend that physicians spend at least six to 10 minutes closely examining the colon lining for polyps during the procedure's withdrawal phase.
"Only by understanding the limitations of colonoscopy can we improve its use and ability to detect polyps and thereby reduce the burden of colorectal cancer," he said.