[631] Filiform Serrated Adenoma Is an Unusual Pathologic Variant of Traditional Serrated Adenoma.

Sang Y Ha, Jae J Lee, Soo M Ahn, Cheol K Park, Kyoung M Kim. Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

Background: Filiform serrated adenoma (FSA) is an uncommon type of polyp that shows dysplastic morphologic features similar to traditional serrated adenoma (TSA). Unlike TSA, FSA is composed predominantly of prominent, thin, elongated filiform projections lined by neoplastic epithelium with serrated contour. However, it is not established that this type of polyp with unique morphology has the same pathogenesis as TSA or not.
Design: Thirteen FSAs were retrospectively identified by review of colonic polyp biopsy which contained the term “serrated” in the final diagnosis between 2001 and 2007. Mutation analysis of BRAF and KRAS genes was performed by using PCR and direct sequencing. Methylation-specific PCR was performed to detect promoter hypermethylation of hMLH1, MGMT, p16, MINT1, MINT2, MINT31 and APC genes. The CpG island methylator phenotype (CIMP) was recorded as negative if ≤1 locus was methylated, low if 2 or 3 loci were methylated, and high if 4 loci were methylated. Microsatellite instability (MSI) was evaluated by using five quasimonomorphic markers. Allelic size variations found in 1-2 microsatellites were classified as MSI-low and ≥3 microsatellites were considered MSI-high. The clinicopathologic and molecular results were compared to our previously published TSA data.
Results: Thirteen polyps were obtained from 13 patients including eight men and five women, with a mean age of 55 years (range: 44-72 y). Twelve polyps were found in the left colon and one in the right colon. Seven patients had more than one polyp in the colon at the time of initial colonoscopy. One patient had metachronous adenocarcinoma detected in the colon at a different anatomic site from the polyp. All but one FSA showed low-grade dysplasia and one with high- grade dysplasia. No carcinomatous transformation was observed. BRAF and KRAS mutation was observed in six (46.2%) and four (30.3%) polyps, respectively, and they were mutually exclusive. Hypermethylation of hMLH1, MGMT, p16, MINT1, MINT2, MINT31 and the APC gene was found in 30.3%, 38.5%, 15.4%, 53.8%, 46.2%, 38.5% and 15.4%, respectively. FSAs were classified as CIMP-negative in three (23.1%), CIMP-low in five (38.5%), CIMP-high in five (38.5%) cases. All polyps were microsatellite stable.
Conclusions: FSA occurs predominantly in the left colon. Unlike TSA, FSA shows more frequent KRAS mutations, and less frequent BRAF mutation and promoter hypermethylation. These molecular findings are similar to TSA located in the left colon. Although the histologic findings are unique, FSA can be categorized as an unusual pathologic variant of TSA.
Category: Gastrointestinal

Wednesday, March 2, 2011 9:30 AM

Poster Session V # 27, Wednesday Morning


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