MLH1-Deficient Ovarian and Endometrial Carcinomas Most Often Result from Epigenetic Silencing of MLH1 by Promoter Hypermethylation and Do Not Harbor BRAF V600E Mutations: Implications for Identifying Patients with Lynch Syndrome (LS).
Jonathan Kitayama, Teri A Longacre, Sofia Liou, Lisa Ma, Daniel Arber, Reetesh K Pai. Stanford University, CA
Background: Mismatch repair (MMR) protein abnormalities occur in both sporadic gynecologic carcinomas and carcinomas from persons with Lynch syndrome (LS). Gynecologic carcinomas may acquire epigenetic alterations, including hypermethylation of the MLH1 gene promoter, resulting in microsatellite instability. In colorectal carcinoma, 80% of tumors with deficient MLH1 immunohistochemical expression result from MLH1 promoter hypermethylation which is strongly associated with BRAF V600E mutation. We investigated the incidence of MLH1 promoter hypermethylation and BRAF V600E mutations in MLH1-deficient gynecologic carcinomas.
Design: We retrospectively examined 381 ovarian and endometrial carcinomas from 1997 to 2010 for MMR protein abnormalities by immunohistochemistry for MLH1 (clone G168-728, BD PharMingen), MSH2 (clone FE11, Oncogene), MSH6 (clone 44, BD Transduction), and PMS2 (clone MRQ-28, CellMarque). Carcinomas with concurrent loss of expression of MLH1 and PMS2 were analyzed for the V600E mutation of the BRAF gene by real-time PCR and post-PCR allelic discrimination melting curve analysis and MLH1 promoter methylation using real-time PCR (Methylight) for quantitative DNA methylation analysis, as described (Weisenberger DJ et al. Nature Genetics 2006; 38: 787).
Results: Fifty-six of 381 (15%) carcinomas demonstrated loss of MLH1 and PMS2 expression with a median age of 63 years (range 42 to 86 years). None of the 56 cases demonstrated a BRAF V600E mutation. MLH1 promoter hypermethylation was identified in 54/56 (96%) carcinomas. Two carcinomas, one ovarian endometrioid carcinoma diagnosed at 55 years and one endometrial mucinous carcinoma diagnosed at 56 years, demonstrated an absence of MLH1 promoter hypermethylation.
Conclusions: MLH1 protein deficiency occurs frequently in endometrial carcinomas and is almost always caused by epigenetic silencing of MLH1 due to hypermethylation of its promoter region. In contrast to colorectal carcinoma, routine screening for MLH1 protein deficiency in gynecologic carcinomas may not be effective in selecting patients for germline genetic testing for LS. In addition, BRAF V600E mutation analysis is not useful in distinguishing sporadic gynecologic carcinomas from carcinomas in persons with LS. When identified, MLH1-deficient gynecologic carcinomas should be tested for MLH1 promoter hypermethylation, although such analysis will not distinguish rare carcinomas with constitutional (germline) MLH1 epimutation.
Category: Gynecologic & Obstetrics
Wednesday, March 2, 2011 1:00 PM
Poster Session VI # 162, Wednesday Afternoon