title: Somatic aberrations of mismatch repair genes as a cause of microsatellite-unstable cancers.
abstract: Lynch syndrome (LS) is caused by germline mutations in mismatch repair (MMR) genes, resulting in microsatellite-unstable tumours. Approximately 35% of suspected LS (sLS) patients test negative for germline MMR gene mutations, hampering conclusive LS diagnosis. The aim of this study was to investigate somatic MMR gene aberrations in microsatellite-unstable colorectal and endometrial cancers of sLS patients negative for germline MMR gene mutations. Suspected LS cases were selected from a retrospective Clinical Genetics Department diagnostic cohort and from a prospective multicentre population-based study on LS in The Netherlands. In total, microsatellite-unstable tumours of 40 sLS patients (male/female 20/20, median age 57 years) were screened for somatic MMR gene mutations by next-generation sequencing. In addition, loss of heterozygosity (LOH) of the affected MMR genes in these tumours as well as in 68 LS-associated tumours and 27 microsatellite-unstable tumours with MLH1 promoter hypermethylation was studied. Of the sLS cases, 5/40 (13%) tumours had two pathogenic somatic mutations and 16/40 (40%) tumours had a (likely) pathogenic mutation and LOH. Overall, LOH of the affected MMR gene locus was observed in 24/39 (62%) tumours with informative LOH markers. Of the LS cases and the tumours with MLH1 promoter hypermethylation, 39/61 (64%) and 2/21 (10%) tumours, respectively, demonstrated LOH. Half of microsatellite-unstable tumours of sLS patients without germline MMR gene mutations had two (likely) deleterious somatic MMR gene aberrations, indicating their sporadic origin. Therefore, we advocate adding somatic mutation and LOH analysis of the MMR genes to the molecular diagnostic workflow of LS.
authors.affiliation: Department of Pathology, Erasmus MC Cancer Institute, University Medical Centre, Rotterdam, The Netherlands.
authors.forename: Willemina R R
authors.initials: WR
authors.lastname: Geurts-Giele
authors.forename: Celine H M
authors.initials: CH
authors.lastname: Leenen
authors.forename: Hendrikus J
authors.initials: HJ
authors.lastname: Dubbink
authors.forename: Isabelle C
authors.initials: IC
authors.lastname: Meijssen
authors.forename: Edward
authors.initials: E
authors.lastname: Post
authors.forename: Hein F B M
authors.initials: HF
authors.lastname: Sleddens
authors.forename: Ernst J
authors.initials: EJ
authors.lastname: Kuipers
authors.forename: Anne
authors.initials: A
authors.lastname: Goverde
authors.forename: Ans M W
authors.initials: AM
authors.lastname: van den Ouweland
authors.forename: Margot G F
authors.initials: MG
authors.lastname: van Lier
authors.forename: Ewout W
authors.initials: EW
authors.lastname: Steyerberg
authors.forename: Monique E
authors.initials: ME
authors.lastname: van Leerdam
authors.forename: Anja
authors.initials: A
authors.lastname: Wagner
authors.forename: Winand N M
authors.initials: WN
authors.lastname: Dinjens
mesh_terms: D000328:Adult; D000368:Aged; D053843:DNA Mismatch Repair / Q000235:genetics*; D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D019656:Loss of Heterozygosity; D055847:Lynch Syndrome II / Q000175:diagnosis* / Q000235:genetics*; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D060885:Multiplex Polymerase Chain Reaction; D009154:Mutation
keywords: Lynch syndrome; colorectal cancer; germline mutation; mismatch repair deficiency