[725] Benign Fibroblastic Polyps (Mucosal Perineuriomas) Harbor BRAF Mutations, but Not in the Stromal Component: A Laser Capture Microdissection Study

Jason R Pettus, Joel A Lefferts, Stephanie Schulte, Dhanpat Jain, Robert D Odze, Amitabh Srivastava. Dartmouth-Hitchcock Medical Center, Lebanon, NH; Yale University School of Medicine, New Haven, CT; Brigham & Women's Hospital, Boston, MA

Background: Benign fibroblastic polyps (BFP) of the colon, also termed mucosal perineuriomas, are rare mucosal lesions characterized by a bland spindle cell proliferation within the lamina propria of a polyp with hyperplastic/serrated features. A high prevalence of BRAF V600E mutation has been reported in BFPs, which suggests that they may be peculiar variants of hyperplastic or sessile serrated polyps of the colon. We analyzed a series of BFPs for BRAF mutations in the entire polyp, and separately in microdissected polyp stroma, to determine whether the stromal component is part of the same clone.
Design: The pathology archives of three academic hospitals were searched for cases diagnosed as BFP and mucosal perineurioma. H&E slides were reviewed to confirm the diagnosis in each case. Polyps with insufficient stroma for microdissection and those without a definite serrated epithelial component were excluded from the study. DNA was extracted from formalin-fixed paraffin embedded tissue from each polyp and analyzed for BRAF V600E mutation. The stromal component from BRAF mutation-positive polyps was then microdissected by laser capture microdissection and tested separately for BRAF mutation.
Results: Fourteen cases were considered satisfactory for inclusion in the study based on the amount of lesional stroma in the polyps. The epithelial component of all polyps showed morphologic features of a hyperplastic polyp. The stromal component was positive for EMA (epithelial membrane antigen) by immunohistochemistry in 7/8 cases for which the data was available. Adequate DNA was extracted in 11/14 cases and a BRAF V600E mutation was detected in 8/11 (73%) polyps. Microdissected stromal DNA sufficient for BRAF mutation analysis was extracted in 5 of these 8 cases and showed wild-type BRAF in all five cases (100%) analyzed.
Conclusions: BFPs show a high prevalence of BRAF mutation which, in conjunction with morphology, supports their relationship to colonic serrated polyps. Furthermore, the stromal component appears to be consistently negative for BRAF mutation. “Stroma-rich serrated polyp” more accurately describes the biologic nature of these unique lesions.
Category: Gastrointestinal

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 65, Tuesday Afternoon

 

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