[683] Longitudinal Outcome Study of Sessile Serrated Adenomas of the Colorectum: Sessile Serrated Adenomas of the Colorectum Are Associated with Increased Risk for Subsequent Right-Sided Colorectal Adenocarcinoma

F Lu, DL Webber, D van Niekerk, D Owen, S Tha, D Turbin. University of British Columbia, Vancouver, Canada

Background: Colonic sessile serrated adenomas (SSA) have a significant incidence of high microsatellite instability (MSI-H), and are associated with MSI-H colorectal carcinoma (CRC), developing through the 'mutator pathway' of carcinogenesis. SSA is currently managed in the same fashion as adenomatous polyps (AP). Our aim was to study the natural history of SSA by analyzing retrospectively the outcome of previously undiagnosed SSA and compare it to that of hyperplastic polyps (HP) and AP.
Design: All colorectal polyps diagnosed between 1980 and 2001 as HP were selected from the UBC Hospital archive. Cases chosen as possible SSA were additionally reviewed by 3 pathologists and only those diagnosed as SSA by all 3 pathologists were included. For each subject with SSA, control HP and AP subjects were chosen. Control subjects were matched for age, gender and year-of-diagnosis. Control subjects were also free of a previous or concomitant diagnosis of CRC or AP with high grade dysplasia (HGD). Clinical follow-up was obtained for each SSA and control subject.
Results: A total of 1402 colorectal polyps diagnosed as HP were examined. 81 (5.8%) polyps in 55 subjects were diagnosed as SSA. Of the 40 SSA subjects without a history of CRC or AP with HGD, 6 (15%) developed subsequent CRC or AP with HGD, 5 of these being CRC. The average time to subsequent CRC or AP with HGD was 8.3 years. The incidence of subsequent CRC was significantly higher in the SSA subjects than in the control HP (12.5% vs. 1.8%, p=0.021, Barnard's exact, one sided) and AP subjects (12.5% vs. 1.8%, p=0.021). The SSA associated with subsequent CRC or AP with HGD were mostly located in the distal colon. However, in contrast to the control HP and AP, all of the subsequent CRC or AP with HGD associated with SSA developed in the proximal colon, with 4 of the 5 CRC having a MSI-H phenotype.
Conclusions: The SSA in this study were high risk lesions, with 15% of the SSA subjects developing subsequent CRC or AP with HGD, the majority being right-sided CRC of MSI-H phenotype. This incidence was higher than that of the control HP and AP subjects, and would support the current follow-up of SSA similar to AP, with a strong suggestion that patients harboring them be followed even more closely, and with special attention to examination of the proximal colon.
Category: Gastrointestinal

Monday, March 22, 2010 9:30 AM

Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 97, Monday Morning


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