[694] Gallbladder Adenomas Frequently Harbor Mutations Which Are Uncommon in Gallbladder Adenocarcinomas

A Mojtahed, RK Pai, RK Pai. Stanford University, Stanford, CA; Washington University, St. Louis, MO

Background: The role of gallbladder adenomas in the pathogenesis of gallbladder adenocarcinoma is still controversial. The purpose of this study was to evaluate gallbladder adenocarcinomas, adenoma, and dysplastic lesions for BRAF and KRAS mutations, as well as mismatch repair protein (MMR) abnormalities, to provide insight into the potential role of adenomas as precursor lesions to adenocarcinoma.
Design: We analyzed 29 gallbladder carcinomas (9 papillary and 20 non-papillary), 16 adenomas (6 pyloric, 3 intestinal, 3 biliary, 3 mixed pyloric-biliary, and 1 mixed pyloric-intestinal), and 5 high-grade dysplastic lesions. DNA was extracted from paraffin sections, using the DNease Tissue Kit (Qiagen, CA). Manual microdissection was performed to exclude overabundance of non-lesional tissues. Mutant KRAS was detected using a validated KRAS mutation kit (Mutector II, TrimGen, MD) that identifies somatic mutations located in codons 12 and 13. PCR amplification was performed on PTC-200 cyler (MJ Research, MA). The mutation was detected on an Applied Biosytems 3100. Mutations in codon 600 of BRAF were detected by real-time PCR and post-PCR allelic discrimination melting curve analysis. MMR immunohistochemistry for MLH1, MSH2, MSH6, and PMS2 was also performed.
Results: Gallbladder adenocarcinomas and high-grade dysplastic lesions infrequently harbored KRAS (2/29 and 0/5) or BRAF (0/29 and 0/5) mutations (Table 1). Compared with adenocarcinomas, adenomas frequently harbored KRAS codon 12 mutations (5/16) and BRAF mutations (1/16) (p = 0.01). Adenomas with pyloric-type histology more often harbored KRAS mutations (4/10) compared with other histologic subtypes (1/6). Both adenomas and adenocarcinomas displayed intact expression of MMR proteins.

Table 1. Summary of KRAS, BRAF, and Mismatch Repair Protein Analysis
Histologic DiagnosisNo. of CasesKRAS Codon 12 MutationKRAS Codon 13 MutationBRAF V600E MutationIntact MMR IHC
Pyloric or mixed pyloric-type1040110
High-grade Dysplasia5000Not Done

Conclusions: The presence of frequent KRAS and BRAF mutations in gallbladder adenomas compared with gallbladder adenocarcinomas suggests that adenomas and adenocarcinomas arise through distinct molecular pathways.
Category: Gastrointestinal

Tuesday, March 23, 2010 9:30 AM

Poster Session III # 132, Tuesday Morning


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