Flat, non-polyploid colorectal neoplasms (NP-CRNs) are difficult to detect, but when examined, they appear to be common. Additionally they may have a stronger association with colorectal cancer than polyps, which are more routinely observed in examination, according to a study published on March 5, 2008 in JAMA

Colorectal cancer, sometimes simply called colon cancer, encompasses cancerous growths in the large intestines and appendix. It is the second leading cause of cancer death in the United States. Prevention strategies have focused on detecting and removing polyploid neoplasms, which are abnormal growths resembling polyps. More recently, however, it has been shown that colorectal cancer can develop from NP-CRNs, which are flat or depressed in shape. These can be more difficult to detect, according to the authors of the study: "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."

Since information is limited regarding the true significance of NP-CRNs in colorectal cancer development, Roy M. Soetikno, M.D., M.S., and colleagues with the Veterans Affairs Palo Alto Health Care System, Palo Alto, California, investigated data from 1,819 patients undergoing elective colonoscopy, in the hope of estimating the frequency of NP-CRNs and to characterize the relationship of NP-CRNs to colorectal cancer.

Patients were also classified into subgroups according to their situations: the screening group, of asymptomatic patients who had undergone average risk-screening colonoscopies; the surveillance group, who had a personal or hereditary history of colorectal cancer; or the symptomatic group, who showed symptoms and indications associated with colorectal neoplasms, including anemia, rectal bleeding, constipation, diarrhea, positive results from a fecal occult blood test, weight loss, abdominal pain, and inflammatory bowel disease.

In the whole group, NP-CRNs were present in 9.35% of patients. According to subpopulation, the screening group showed 5.84%, surveillance showed 5.84%, and symptomatic showed 6.01%. In cancers that had not spread, or had spread in the tissue beneath the mucous membrane the overall prevalence was 0.82%, while prevalence in the screening population was 0.32%. It was also observed in the surveillance and screening populations.

Overall, NP-CRNs were almost 10 times more likely to contain cancerous tissue than polyploid lesions, regardless of size. The depressed type of NP-CRNs showed the highest risk (33%.) NP-CRNs containing cancer were generally smaller in diameter when compared with polyploid cancerous regions.

"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," write the authors.

Editorial: Nonpolypoid Colorectal Neoplasia in the United States

David Lieberman, M.D., of Oregon Health & Science University, Portland VA Medical Center, Portland, Ore., contributed an additional editorial in which he 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."

Prevalence of Nonpolypoid (Flat and Depressed) Colorectal Neoplasms in Asymptomatic and Symptomatic Adults
Roy M. Soetikno; Tonya Kaltenbach; Robert V. Rouse; Walter Park; Anamika Maheshwari; Tohru Sato; Suzanne Matsui; Shai Friedland
JAMA. 2008; 299(9):1027-1035.
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Nonpolypoid Colorectal Neoplasia in the United States: The Parachute Is Open
David Lieberman
JAMA. 2008; 299(9):1068-1069.
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Written by Anna Sophia McKenney