title: Immunohistochemical staining for p16 and BRAFV600E is useful to distinguish between sporadic and hereditary (Lynch syndrome-related) microsatellite instable colorectal carcinomas.
abstract: DNA mismatch repair (MMR) protein analysis by immunohistochemistry (IHC) can identify colorectal cancer (CRC) with microsatellite instability (MSI). As MLH1-deficient CRC can be hereditary or sporadic, markers to distinguish between them are needed. MLH1 promoter methylation assay is the reference method; however, sometimes, it is challenging on formalin-fixed paraffin-embedded tissue samples. We assessed by IHC the expression of BRAFV600E, p16, MGMT, and CDX2 in 55 MLH1-deficient MSI CRC samples (of which 8 had a germline MLH1 mutation) to determine whether this panel differentiates between sporadic and hereditary CRCs. We also analyzed MLH1 promoter methylation by methylation-specific PCR and pyrosequencing and BRAF status by genotyping. None of the hereditary CRCs showed MLH1 methylation, BRAF mutation, BRAFV600E-positive immunostaining, or loss of p16 expression. We detected MLH1 promoter methylation in 67 % and a BRAF mutation in 42 % of CRC, all showing MLH1 promoter methylation. BRAFV600E IHC and BRAF genotyping gave concordant results in all but two samples. Loss of expression of p16 was found in 30 % of CRC with methylation of the MLH1 promoter, but its expression was retained in all non-methylated and part of MLH1-methylated tumors (100 % specificity, 30 % sensitivity). CDX2 and MGMT expression was not associated with MLH1 status. Thus, BRAFV600E and p16 IHC may help in differentiating sporadic from hereditary MLH1-deficient CRC with MSI. Specifically, p16 IHC might be used as a surrogate marker for MLH1 promoter methylation, because all p16-negative CRCs displayed MLH1 methylation, whereas hereditary CRCs were all p16-positive.
authors.affiliation: Pathology Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France. Florence.Boissiere@icm.unicancer.fr.|Translational Research Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France. Florence.Boissiere@icm.unicancer.fr.
authors.forename: Florence
authors.initials: F
authors.lastname: Boissière-Michot
authors.affiliation: Pathology Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Frugier
authors.affiliation: Translational Research Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Ho-Pun-Cheung
authors.affiliation: Translational Research Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France.
authors.forename: Evelyne
authors.initials: E
authors.lastname: Lopez-Crapez
authors.affiliation: Oncogenetic Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Duffour
authors.affiliation: Pathology Department, Institut Régional du Cancer de Montpellier, 208 rue des Apothicaires, 34 298, Montpellier Cedex 5, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Bibeau
mesh_terms: D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000175:diagnosis / Q000235:genetics* / Q000378:metabolism*; D019175:DNA Methylation / Q000235:genetics; D019942:Genes, p16; D005838:Genotype; D018095:Germ-Line Mutation / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D053842:Microsatellite Instability; D018895:Microsatellite Repeats / Q000235:genetics; D009154:Mutation / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D013194:Staining and Labeling / Q000379:methods
chemical_list: C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf
keywords: Immunohistochemistry; Lynch syndrome; MSI; Promoter methylation; Surrogate markers