[627] Prevalence of Different Polyp Types in MSI and MSS Age and Gender Matched Cohorts of Colorectal Cancer Resections

David Gibbons, Chee H Ng, Robert Geraghty, Elizabeth Rinehart, John Hyland, Ronan P O'Connell, Des Winter, Hugh Mulcahy, Glen Doherty, Diarmuid O'Donoghue, Fennelly David, Sheahan Kieran. St Vincent's University Hospital, Dublin, Ireland; Brigham and Women's Hospital, Boston, MA

Background: The sessile serrated pathway has gained increased recognition in recent years. Up to 30% of colorectal tumours are thought to arise in this manner. The significance of sessile serrated adenomas (SSAs) in this pathway is being elucidated. We sought to establish the prevalence and significance of this finding in curative resections for colorectal carcinoma.
Design: All colorectal carcinomas resected with curative intent, with immunohistochemical characterization of microsatellite status at diagnosis, over an eight year period were identified. 1415 colectomy specimens were identified of which 126 had microsatellite instability (MSI). An age and gender matched MSS cohort was generated. A careful gross examination described and sampled all polyps. All polyps were reviewed, enumerated and classified as SSA (sessile serrated adenoma), adenoma or hyperplastic. Appendiceal polyps were excluded. Mean numbers of polyps, total and subtypes were compared in the MSI and MSS groups. A two-tailed t-test was used.
Results: 57% of MSI cases and 50% of MSS cases had polyps in the resection. In MSI cases there were a total of 5 SSAs, 92 adenomas and 37 hyperplastic polyps, total = 134. In MSS cases there were 0 SSAs, 62 adenomas and 23 hyperplastic polyps, total = 95. There was no significant difference in numbers of adenomas, hyperplastic polyps or total polyps in both groups. However there were significantly more SSAs in the MSI group (p=0.0239).

Polyp Numbers in MSI and MSS Resections
Total Polyps13485

Conclusions: Although absolute numbers are low, the finding of an SSA in a cancer colectomy specimen is a strong indicator that the carcinoma will be microsatellite unstable (MSI).
Category: Gastrointestinal

Monday, March 4, 2013 1:00 PM

Poster Session II # 136, Monday Afternoon


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