Colonoscopy is the single best option for identifying signs of colorectal cancer, but the technology isn't perfect. New research shows the procedure misses the signs in as many as 1 in 20 patients, with 6 percent of colorectal cancers diagnosed within three to five years after someone receives a clean colonoscopy report.
The population-based study, by researchers from Huntsman Cancer Institute at the University of Utah, suggests some cases are overlooked at the time of colonoscopy or develop rapidly between colonoscopies and are therefore referred to as "missed" colorectal cancers.
That three- to five-year timeframe is well with the 10 years recommended between colonoscopies for colorectal cancer screening for most people, as well as the five years indicated for people at increased risk, according to the study published online in the journal Gastroenterology.
"Not only did we find that colonoscopy isn't perfect, we discovered a number of factors associated with these 'missed' cancers," said lead researcher N. Jewel Samadder. "They tended to appear in patients over the age of 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 at the far end of the colonoscopy’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," said Samadder. "However, the medical records of the patients with missed cancers showed these problems were seldom present."
The findings are based on an analysis of medical records for more than 85 percent of Utah's population over between 1995 and 2009.
Samadder said the study underscores the need for physicians and patients to communicate prior to the procedure to ensure that a complete medical history — accounting for older age, family history of colorectal cancer, and prior history of polyps — is known so extra time and care can be taken during the procedure, particular in patients who face higher-than-average risks for the disease.
"This is not entirely a quality of care issue," Samadder said. "Our findings implicate genetic and biological issues associated with having previous polyps and having a family history of colorectal cancer."
Many organizations, such as the American Society of Gastroenterologists, recommend that physicians spend at least 6-10 minutes closely examining the colon lining for polyps during the procedure's withdrawal phase (where they have reached the end of the colon and are beginning to come out).
"Only by understanding the limitations of colonoscopy," Samadder said, "can we improve its use and ability to detect polyps and thereby reduce the burden of colorectal cancer."
The study was funded, in part, by the National Cancer Institute.
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