A study published in the Journal of the American Medical Association said flat, non-polypoid colorectal neoplasms appear to be relatively common and may be more likely to develop into cancer compared with the more routinely diagnosed type of colorectal polyps, the AMA said Wednesday in a news release.

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

"Non-polypoid 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)," the study's authors said. "As compared with surrounding normal mucosa, NP-CRNs appear to be slightly elevated, completely flat, or slightly depressed."