A new study finds that colonoscopies may in fact sometimes miss pre-cancerous lesions that are a sign of the condition.

Non-polypoid colorectal neoplasm (NP-CRN), how these precancerous lesion are called, are a type of flat lesion that are often missed by the procedure, meaning that if it is not detected, it can not be removed, thus allowing for it to grow and maybe even to become cancerous.

Dr. Roy M. Soetikno and colleagues with the Veterans Affairs Palo Alto Health Care System found the non-polypoid colorectal neoplasm were nearly 10 times more likely to contain cancerous tissue than polypoid lesions.

“Non-polypod colorectal neoplasms are more difficult to detect by colonoscopy or computed tomography colonography because the subtle findings can be difficult to distinguish from those of normal mucosa (membrane). As compared with surrounding normal mucosa, NP-CRNs appear to be slightly elevated, completely flat, or slightly depressed,” the study’s authors said.

For the study, Dr. Soetikno and his colleagues have examined data from a group of 1,819 patients undergoing elective colonoscopy to estimate the prevalence of NP-CRNs and to characterize the association of NP-CRNs with colorectal cancer. One third of the patients were coming in for routine screening. The rest had symptoms such as bleeding or pain, or were being screened because they had previous polyps or a family history of colon cancer.

"Future studies on NP-CRNs should further evaluate whether the diagnosis and removal of NP-CRNs has any effect on the prevention and mortality of colorectal cancer and particularly focus on their genetic and protein abnormalities," Soetikno and his team concluded.

David Lieberman of the Oregon Health and Science University said in an accompanying editorial that the study underlined the importance of quality in the performance of colonoscopy. He also added that more work needs to be done on the imaging from colonoscopies to better detect the NP-CRNs and to see whether patients with these types of lesions require more intense colonoscopic tests.

The study’s findings come during a month dedicated to raise people’s awareness on what leads to colorectal cancer and what can be done to avoid the disease as much as possible. An accurate screening and a diet based more on fruits and vegetables seem to be the perfect way to stay away from trouble, health experts say.

Colon cancer is the second most common cause of cancer-related deaths in the U.S., with more than 56,000 people losing the battle each year. The American Cancer Society estimates almost 150,000 new cases of colorectal cancer for 2008 in the U.S.

The study was published in the March 5 issue of the Journal of the American Medical Association.