title: Prevalence of somatic mutl homolog 1 promoter hypermethylation in Lynch syndrome colorectal cancer.
abstract: BACKGROUND
  Colorectal cancers (CRCs) that have microsatellite instability (MSI) and mutL homolog 1 (MLH1) immunoloss are observed in 3 clinical scenarios: Lynch syndrome (LS), sporadic MSI CRC, and Lynch-like syndrome (LLS). v-Raf murine sarcoma viral oncogene homolog B1 (BRAF) mutational analysis is used to differentiate LS from sporadic MSI CRC. The role of MLH1 promoter methylation status for the differential diagnosis of these clinical forms is not well established. The objectives of this study were: 1) to analyze MLH1 promoter methylation in MLH1-deficient CRCs by pyrosequencing, and 2) to assess its role in the differential diagnosis of MLH1-deficient CRCs.
  
  
  METHODS
  In total, 165 CRCs were analyzed, including LS (n = 19), MSI BRAF-mutated CRC (n = 37), MSI BRAF wild-type CRC (n = 60), and a control group of CRCs without MSI (microsatellite stable [MSS] CRC; n = 49). MLH1 promoter methylation status was analyzed by pyrosequencing, and the ability of different strategies to identify LS was assessed.
  
  
  RESULTS
  The average ± standard deviation methylation in LS (9% ± 7%) was significantly lower than that in MSI BRAF-mutated CRC (42% ± 17%; P < .001) and in MSI BRAF wild-type CRC (25% ± 19%; P = .002). Somatic MLH1 hypermethylation was detected in 3 patients (15.8%) with LS, in 34 patients (91.9%) with MSI BRAF-mutated CRC, and in 37 patients (61.7%) with MSI BRAF wild-type tumors. Patients with MSI BRAF wild-type, unmethylated tumors (ie, LLS) had a stronger family history of CRC than those who had tumors with MLH1 methylation (P < .05). The sensitivity for ruling out LS was 100% for BRAF analysis, 84.2% for MLH1 methylation analysis, and 84.2% for the combination of both analyses.
  
  
  CONCLUSIONS
  Somatic MLH1 promoter methylation occurs in up to 15% of LS CRCs. Somatic BRAF analysis is the most sensitive strategy for ruling out LS. Patients who have CRCs with loss of MLH1 protein expression and neither BRAF mutation nor MLH1 methylation resemble patients with LS.
authors.affiliation: Department of Gastroenterology, Barcelona Hospital Clinic, Networked Biomedical Research Center on Hepatic and Digestive Diseases (CIBERehd), August Pi i Sunyer Biomedical Research Institute (IDIBAPS), University of Barcelona, Barcelona, Catalonia, Spain.
authors.forename: Leticia
authors.initials: L
authors.lastname: Moreira
authors.forename: Jenifer
authors.initials: J
authors.lastname: Muñoz
authors.forename: Míriam
authors.initials: M
authors.lastname: Cuatrecasas
authors.forename: Isabel
authors.initials: I
authors.lastname: Quintanilla
authors.forename: Maria Liz
authors.initials: ML
authors.lastname: Leoz
authors.forename: Sabela
authors.initials: S
authors.lastname: Carballal
authors.forename: Teresa
authors.initials: T
authors.lastname: Ocaña
authors.forename: María
authors.initials: M
authors.lastname: López-Cerón
authors.forename: Maria
authors.initials: M
authors.lastname: Pellise
authors.forename: Sergi
authors.initials: S
authors.lastname: Castellví-Bel
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Jover
authors.forename: Montserrat
authors.initials: M
authors.lastname: Andreu
authors.forename: Angel
authors.initials: A
authors.lastname: Carracedo
authors.forename: Rosa Maria
authors.initials: RM
authors.lastname: Xicola
authors.forename: Xavier
authors.initials: X
authors.lastname: Llor
authors.forename: Clement Richard
authors.initials: CR
authors.lastname: Boland
authors.forename: Ajay
authors.initials: A
authors.lastname: Goel
authors.forename: Antoni
authors.initials: A
authors.lastname: Castells
authors.forename: Francesc
authors.initials: F
authors.lastname: Balaguer
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000453:epidemiology / Q000235:genetics*; D019175:DNA Methylation; D005260:Female; D006801:Humans; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009687:Nuclear Proteins / Q000235:genetics*; D015995:Prevalence; D011401:Promoter Regions, Genetic; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C501486:MLH1 protein, human; D009687:Nuclear Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D000070957:MutL Protein Homolog 1
keywords: CpG island methylator phenotype; Lynch syndrome; colorectal cancer; methylation; microsatellite instability; mutL homolog 1; v-Raf murine sarcoma viral oncogene homolog B1