Colonoscopies Are Not a Perfect Tool

Colon cancers sometimes missed on colonoscopy or grew very quickly after screening

(RxWiki News) More people are taking advantage of colonoscopies, the best tool for detection of colon cancer. However, not everyone who has the screening can be completely certain they are cancer-free.

A small number of the people who followed recommendations for colonoscopy screening every decade starting at age 50 still presented with colon cancer in the time between screenings, researchers have found.

Whether this finding was because the tumor was missed on colonoscopy or was exceptionally fast growing is not known, these researchers admitted.

High-risk factors for interim colon cancers (those found in the interim between the first colonoscopy and second, a decade later) included having a family history of colon cancer, being older than 65 and having been identified as having polyps, the researchers revealed.

"Talk to your doctor about having regular screenings for colon cancer."

These researchers were led by N. Jewel Samadder, MD, MSc, of the Huntsman Cancer Institute in Salt Lake City. They looked at data from patients aged 50 to 80 years who had a colonoscopy at Intermountain Healthcare and University of Utah Healthcare from 1995 to 2009. The researchers also looked at the Utah Population Database, which provided information on patients who developed colorectal cancer and those with a family history of the disease.

A total of 126,851 people underwent colonoscopies and met the study criteria, and 2,659 were diagnosed with colorectal cancer.

The researchers found that 6 percent of those with colorectal cancer (159 patients) were diagnosed with cancer six to 60 weeks after having a colonoscopy.

More than half (57 percent) of these patients were identified as having non-cancerous polyps at their colonoscopy, while 36 percent of patients had polyps and were found to have cancer at colonoscopy. Furthermore, 26 percent of those with polyps did not develop cancer at all.

Polyps are growths on the lining of the colon.

The study's authors also found that those diagnosed with cancer after a previous colonoscopy generally had earlier-staged cancers, and these patients had a lower risk of death.

The cancerous tumors found in these patients were also more likely to be on the right side of the colon (which is at the far end of where the colonoscope reaches), where tumors are typically flatter and fast growing, and sometimes difficult to detect.

The study's authors admitted potential problems with their study, such as lacking information on the quality of the bowel preparation, but also noted that their study had many strengths, including that the procedure was carried out by gastroenterologists (physicians trained in the digestive system).

They concluded that additional studies are needed to determine if the cancers found between screenings are biologically different from the other tumors.

"Only by understanding the limitations of colonoscopy," Dr. Samadder said in a press release, "can we improve its use and ability to detect polyps and thereby reduce the burden of colorectal cancer."

Colonoscopies are recommended every decade starting at age 50. For people with a family history of colon cancer, the screening is recommended every five years.

This study appears in the April issue of Gastroenterology.

The authors disclosed that Dr. Randall Burt has been a consultant for Myriad Genetics, and Dr. Samadder has been a consultant for Cook Medical and Covidien, Inc. No other conflicts were disclosed.

Review Date: 
March 21, 2014