Flat Colon Lesions Relatively Common, Associated With Colorectal Cancer

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.

Journal reference: JAMA. 2008;299[9]:1027-1035.  

Editorial: Nonpolypoid Colorectal Neoplasia

In an accompanying editorial, David Lieberman, M.D., of Oregon Health & Science University, Portland VA Medical Center, Portland, Ore., comments on the findings of Soetikno and colleagues.

"[Nonpolypoid colorectal neoplasms] may be biologically distinct from polypoid lesions and appear to be more likely to harbor malignant features. Detection and complete removal at colonoscopy may be challenging. The current study emphasizes the importance of quality in the performance of colonoscopy," he writes. "The optimal methods for enhancing colonoscopic imaging of NP-CRNs are uncertain. ... Additional studies are needed to determine whether imaging modalities such as computed tomography colonography will be able to detect NP-CRNs. Finally, longitudinal studies are needed to determine whether patients with NP-CRNs require more intensive colonoscopic surveillance compared with patients with polypoid lesions of similar size and histology."

Reference for editorial: JAMA. 2008;299[9]:1068-1069.