6% of colorectal cancers developed within 5 years after colonoscopy

Approximately 6% of colorectal cancers are diagnosed within 3 to 5 years after the patient received a colonoscopy, according to findings from a recent population-based study.

Cancers that developed between colorectal screenings were associated with the proximal colon, earlier-stage cancer, lower risk of death, a higher rate of adenoma and a family history of colorectal cancer.

N. Jewel Samadder 

N. Jewel Samadder

“Not only did we find that colonoscopy isn’t perfect, we discovered a number of factors associated with these ‘missed’ cancers,” N. Jewel Samadder, MD, MSc, assistant professor of medicine in the division of gastroenterology at Huntsman Cancer Institute, said in a press release. “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.”

Samadder and colleagues performed a population-based cohort study of Utah residents who underwent colonoscopy examinations from 1995 to 2009 at Intermountain Healthcare or the University of Utah Health System. They examined the proportion, characteristics and factors that predict interval colorectal cancers that develop within 6 to 60 months of colonoscopy,

Colonoscopy results were correlated with cancer histories from the Utah Population Database to classify patients who underwent colonoscopy 6 to 60 months before a diagnosis of colorectal cancer. Researchers performed logistic regression to assess risk factors associated with interval cancers.

Among 126,851 patients who underwent colonoscopies, 2,659 were diagnosed with colorectal cancer; 6% of these colorectal cancers were found to have developed within 6 to 60 months after a colonoscopy.

The percentage of patients who exhibited adenomas at their index colonoscopy was higher among those with interval colorectal cancer (57.2%) than those with colorectal cancer detected at colonoscopy (36%) and those who did not develop cancer (26%; P<.001).

“Cancers in the right side are often biologically different than those in other parts of the colon, arising from different types of polyps,” Samadder said. “These types of polyps are flatter and faster growing, which may explain why they are not seen during colonoscopy as well as how a cancer could develop even when no polyps were visible.”

Interval colorectal cancers were observed to be earlier-stage tumors than those detected at index colonoscopy, and they also were more likely to be proximally located (OR=2.24; P<.001).

Researchers reported that patients with interval colorectal cancer were more likely to have a family history of colorectal cancer (OR=2.27; P=.008) and exhibited a lower risk of death than patients found to have colorectal cancer at colonoscopy (HR=0.63; P<.001).

“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. 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.”

Disclosure: The researchers report no relevant financial disclosures.