Serrated adenoma is a risk factor for subsequent adenomatous polyps

Background: Serrated adenomas (SA) are histologically defined by the presence of both hyperplastic and adenomatous features. These uncommon polyps are thought to play an important role in the development of sporadic colorectal cancers (CRC) with microsatellite instability (MSI). There is paucity of data on the risk of progression of SA to CRC. This study was undertaken to define the relationship between SA and the future development of adenomatous polyps. Methods: Colonoscopic biopsies that contained a pathologic diagnosis of SA were identified from a pathology database of a major urban academic medical center. Those patients with absence of concomitant malignancy, complete colonoscopy, good or adequate prep and presence of at least one follow-up procedures were identified. These were matched to controls by age, sex, indication for colonoscopy, polyp type and number and duration of follow-up. Outcomes of the follow-up procedures were compared. Results: Between January 1997 and June 2005 17,226 colonoscopic biopsies and polypectomies were performed. Of these, 80 patients (0.5%) with SA were found, and of these SA, 80% were found in the left colon. The average age of patients undergoing colonoscopy was 58.5 years, and the average age of patients with SA was 68 years (P = 0.004). Of all patients with SA, 7 (9%) had concomitant CRC. The final groups contained 17 patients and 17 controls, respectively, and were well matched. The mean follow-up interval in the patient group was 29 months vs. 31 months in the control group (P = 0.82). On follow-up examination four patients (24%) and no controls had adenomatous polyps (P = 0.01). Conclusions: While SA are uncommon, they are commonly associated with colorectal cancer. Serrated adenomas appear to be found more commonly in the left colon and in older patients. This study found a significant association between SA and the subsequent development of adenomatous polyps. Further studies are needed to define appropriate preventive strategies for these patients.