According to a new study by researchers in the U.S. colonoscopies do not detect all colorectal cancers; they say that flat lesions can be easily overlooked during a colonoscopy.
The researchers say flat, nonpolypoid colorectal tumours are common and may develop into cancer compared to those most routinely diagnosed type of colorectal polyps.
But they say as flat lesions are hard to find because they merge with surrounding healthy tissues, they are easily overlooked during a colonoscopy.
The scientists from the Veterans Affairs Palo Alto Health Care System, say the risk of colorectal cancer is high for patients who have flat lesions.
Their study examined data from 1,819 patients, almost all men with an average age of 64, from July 2003 to June 2004 undergoing elective colonoscopy to find out how common the flat lesions were and their link with colorectal cancer.
The group were divided into three groups; screening, surveillance and a group of patients with symptoms for colorectal cancer.
Flat lesions were found in 170 people (10%) and the surveillance group had the highest incidence with more than 15% who had flat lesions; approximately six percent of the screening and symptoms groups had flat lesions.
The researchers found that the flat growths were five times more likely to be cancerous than polyps.
Colorectal cancer, also called colon cancer or large bowel cancer, includes cancerous growths in the colon, rectum and appendix.