[583] Sessile Serrated Polyps with Dysplasia: An Immunohistochemical Analysis of 51 Cases

JA Gibson, HP Hahn, RD Odze. Brigham and Women's Hospital, Boston, MA

Background: Sessile serrated polyps (SSP), also termed sessile serrated adenomas, may develop dysplastic changes (SSP-D) believed to represent an intermediate step in the serrated pathway of carcinogenesis in the colon. Recent studies have suggested that some SSP-D show rapid progression to carcinoma. Dysplasia in SSP may show either traditional serrated adenoma (SA) or conventional tubular adenoma (CA) features. However, the biological properties of these two subtypes of SSP-D are unknown. The aim of this study was to evaluate the immunohistochemical properties of SSP-D, with particular emphasis on comparing those with SA versus CA-type dysplasia.
Design: 51 routinely processed SSP-D from 50 patients (mean age: 62 years, M/F ratio: 20/30, 30 right and 21 left colon) obtained via a 4 year pathology database search were evaluated for their location, type of dysplasia (SA or CA) and stained immunohistochemically for Ki67, p53 and beta catenin (for evaluation of their proliferative and molecular properties), MUC 1, 2, 5AC, and 6 (for their mucin differentiation profile) and AMACR (a neoplasia marker). Both the grade and intensity of staining was scored (0-3). Comparisons were made between the SSP-D polyps with SA-type dysplasia versus those with CA-type dysplasia.
Results: 23 SSP-D (45%) contained SA-type, 26 (51%) contained CA-type, and 2 (4%) contained mixed SA/CA-type dysplasia. The mean age of the patients and the size of the lesions were similar. However, a significantly higher proportion of SSP-D with CA-type dysplasia were found in males (54% vs. 26%, P=0.05) and a nearly significant increase in right and transverse colon location was noted as well (78% vs. 48%, p=0.06). Compared to SSP-D with SA-type dysplasia, SSP-D with CA-type dysplasia showed significantly higher aberrant surface Ki67 staining (100% vs 10%, p<0.001) and increased intensity of AMACR expression (strong staining in 83% vs. 0%, p=0.004). Cytoplasmic/nuclear beta catenin positivity was higher in SSP-D with CA-type dysplasia (92% vs. 57%), but not significantly (p=0.10). No differences between the polyp subgroups were noted with regard to MUC1, 2, 5AC, 6 or p53 staining.
Conclusions: SSP-D represent a morphologically heterogeneous group of neoplastic precursor polyps. Those with CA-type dysplasia are more common in males, more frequently found in the right and transverse colon, show higher proliferative rates, and more intense AMACR expression, suggesting that these polyps may have higher neoplastic potential. Further outcome studies of SSP-D with SA vs. CA-type dysplasia should be performed.
Category: Gastrointestinal

Wednesday, March 11, 2009 9:30 AM

Poster Session V # 73, Wednesday Morning