Flat, non-polypoid colorectal neoplasms (NP-CRNs) could have a greater association with cancer compared with the more routinely diagnosed type of colorectal polyps, a new study concluded.

The researchers from the Veterans Affairs Palo Alto Health Care System, Palo Alto, California have published a study in the March 5 issue of JAMA, according to which colorectal cancer can also arise from NP-CRNs.

The problem is that due to their nature, the non-polypoid colorectal neoplasms could be easily missed during the colonoscopy or computed tomography colonography.

“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 his colleagues have 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.

According to their findings, the overall prevalence of NP-CRNs was 9.35 percent. 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. They noted that up to 1 percent of patients who have colonoscopies develop cancer within three years afterward. These missed flat lesions may explain some of these cases, they said.

“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” the authors said.

Colon cancer is the second most common cause of cancer-related deaths in the U.S., with more than 56,000 people losing the battle each year. The American Cancer Society estimates almost 150,000 new cases of colorectal cancer for 2008 in the U.S. The disease affects both men and women equally. Symptoms include changes and bleeding during bowel movements, abdominal pain, severe weight loss, and fatigue.

However, between 2002 and 2004, colon cancer death rates have declined. In men, death rates have dropped 4.9 percent and in women, 4.5 percent, according to an annual report issued by the Nation on the Status of Cancer. The decrease is accredited to better prevention and screening methods.