Flat colon lesions different from polyps are more common and dangerous than previously believed

While most colon neoplasms (adenomas) appear as polyps protruding into the space inside the colon, some lie flat against the colon wall or are even slightly depressed.  A study reported in the Journal of the American Medical Association reports that flat or nonpolypoid colorectal neoplasms (NP-CRNs) are more common that previously believed.

In addition, the flat or depressed lesions were almost ten times as likely to contain cancer than the polyps that protruded.

NP-CRNs are difficult to detect during colonoscopies because they appear very similar to surrounding tissue.  Depressed NP-CRNs that sink into the colon lining are especially hard to find and are the most dangerous.

For the study reported in JAMA,  four specially trained endoscopists at a Veterans Affairs hospital out-patient program in California sprayed the colon with a special blue dye that made the flat lesions easier to see. Over a year’s time, they performed more than 1,800 routine colonoscopies trying to identify how often nonpolypoid colorectal neoplasms occurred.

Patients in the study included a screening group who were having routine colorectal cancer screening, a surveillance group who had a personal or family history of colorectal adenomas or cancer, and a group of people with symptoms of colorectal cancer.  There were about 600 in each group, almost all men with an average age of 64.

Nonpolypoid colorectal neoplasms were found in 170 people, about ten percent of the entire group.   They were more common in the surveillance group where more than 15 percent had a NP-CRN.  About 6 percent of the screening and symptoms groups also had NP-CRNs. 

Roy M. Soetikno, MD, MS and his colleagues wrote,

In this group of veteran patients, NP-CRNs were relatively common lesions diagnosed during routine colonoscopy and had a greater association with carcinoma compared with polypoid neoplasms, irrespective of size.

Three years later, follow-up colonoscopies were done in 68 percent of the 580 patients who were recommended to have one according to guidelines. In those 393 patients, 12 advanced adenomas and 1 new cancer were found, significantly lower percentages than similar studies without the new techniques.

Gastroenterologists doing the colonoscopies for the study developed new skills for recognizing NP-CRN’s by working with leading Japanese endoscopy centers who were already finding and describing NP-CRN’s.  Videos of colonoscopies helped the doctors see changes in color, blood vessels, and colon wall that were characteristic of these lesions. 

In 2000, it became routine practice for doctors in the VA unit where the study was done to use a carmine-indigo spray during colonoscopy when they suspected a NP-CRN.  When they found a lesion, they removed and biopsied it using the endoscope.

Although colonoscopy and removal of polyps prevents many cancers from ever developing, between 0.3 percent and 0.9 percent of patients will develop an interval cancer within the three years after a colonoscopy.  These may be due to missed lesions, incomplete removal of polyps, or fast-growing cancers.  However, the research team believes that NP-CRN’s may also contribute to interval cancers and identifying and removing them may prevent more colorectal cancer.

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The above image shows a NP-CRN (the slightly raised area along the right edge of the first and second pictures) before and after indigo dye was applied.  The third picture is after the position of the colonoscope was changed.  (Images courtesy of the Journal of the American Medical Association)

SOURCE:  Soetikno et al. Journal of the American Medical Association, Volume 299, Number 9, March 5, 2008.

Additional articles about the study and the accompanying editorial appear in Time and the New York Times.

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