Flat Colon Lesions Common, Linked to Colorectal Cancer

Flat, non-polypoid colorectal neoplasms (NP-CRNs), which may be difficult to detect, appear to be relatively common and may have a greater association with cancer compared with the more routinely diagnosed type of colorectal polyps, according to a study in the March 5 issue of JAMA.

Colorectal cancer is the second leading cause of cancer death in the United States. Prevention has focused on the detection and removal of polypoid (resembling a polyp) neoplasms (a new and abnormal growth). Recent studies, however, have demonstrated that colorectal cancer can also arise from NP-CRNs. “Nonpolypoid 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 authors write. Data are limited on the significance of NP-CRNs.

Roy M. Soetikno, M.D., M.S., and colleagues with the Veterans Affairs Palo Alto Health Care System, Palo Alto, Calif., 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.

The overall prevalence of NP-CRNs was 9.35 percent (n = 170). The prevalence of NP-CRNs in the subpopulations for screening, surveillance, and symptoms was 5.84 percent, 15.44 percent, and 6.01 percent, respectively. The overall prevalence of NP-CRNs with cancer that had not spread or had spread in tissue beneath the mucous membrane was 0.82 percent; in the screening population, the prevalence was 0.32 percent. Overall, NP-CRNs were nearly 10 times more likely to contain cancerous tissue than polypoid lesions, irrespective of the size.

The positive size-adjusted association of NP-CRNs with cancer that had not spread or had spread in tissue beneath the mucous membrane was also observed in subpopulations for screening and surveillance. The depressed type of NP-CRNs had the highest risk (33 percent). Nonpolypoid colorectal neoplasms containing cancer were smaller in diameter as compared with the polypoid ones.

“In conclusion, in this population of patients at a single Veterans Affairs hospital, NP-CRNs were a relatively common finding during colonoscopy. They were more likely to contain carcinoma compared with polypoid neoplasms, independent of lesion size. Recent studies have pointed out differences in the genetic mechanisms underlying nonpolypoid and polypoid colorectal neoplasms. 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,” the authors write.

(JAMA. 2008;299[9]:1027-1035. Available pre-embargo to the media at www.jamamedia.org)