Flat colorectal lesions show strong association with invasive carcinoma

Flat or depressed colorectal neoplasms are more likely than polyps to contain in situ or submucosal carcinoma, according to a study released Wednesday. Unfortunately, these nonpolypoid lesions may be missed by colon cancer screening methods, according to gastroenterologists based in Palo Alto, CA.

"Nonpolyoid colorectal neoplasms are more difficult to detect by colonoscopy or CT colonography because the subtle findings can be difficult to distinguish from those of normal mucosa," wrote Dr. Roy Soetikno and colleagues in the Journal of the American Medical Association (2008;299:1027-1035).

The group set out to determine the prevalence of nonpolypoid colorectal neoplasms in 1819 patients who underwent standard colonoscopy screening at the VA Palo Alto Health Care System over a one-year period. Of the 1819 patients, the majority were white men.

The authors pointed out that flat polyps occur most commonly in the Japanese patient population. As a result, a faculty exchange program was undertaken between gastroenterologists and pathologists at the Palo Alto facility and endoscopy centers in Tokyo and Kashiwa, Japan.

Polyps in this study were classified using the Japanese Society for Cancer of the Colon and Rectum classification system: Pedunculated or semipedunculated lesions were considered polypoid, while completely flat or depressed lesions were deemed nonpolypoid.

When appropriate, patients with polyps were treated with biopsy, polypectomy, or surgery. Patients who had one or more polypoid neoplastic lesions removed were followed at one year with another colonoscopy exam for lesion recurrence.

The results showed 42% of the study cohort had at least one superficial colorectal neoplasm. Flat or depressed lesions were diagnosed in 9.35% of that subgroup. The prevalence of flat lesions was 8.58%, while the prevalence of depressed lesions was 0.99%.

"Although nonpolypoid lesions accounted for only 15% of neoplasms, they contributed to 54% of superficial carcinomas," Soetikno's group wrote. "Nonpolypoid morphology was strongly associated with findings of in situ or submucosal invasive carcinoma (odds ratio, 11.1; 95% confidence interval, 4.98-24.8)."

Overall, for patients undergoing colonoscopy screening, the prevalence of nonpolypoid lesions was 5.8%. For those undergoing surveillance, the prevalence jumped to 15.8%. They authors suggested that flat or depressed lesions fall into the pool of polyps that are commonly missed because of incomplete surgical removal or because they are fast-growing interval lesions.

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