title: Strategy in clinical practice for classification of unselected colorectal tumours based on mismatch repair deficiency.
abstract: OBJECTIVE
  Deficiency of DNA mismatch repair (MMR) causes microsatellite instability (MSI) in a subset of colorectal cancers. Patients with these tumours have a better prognosis and may have an altered response to chemotherapy. Some of the tumours are caused by hereditary mutations (hereditary nonpolyposis colon cancer or Lynch syndrome), but most are epigenetic changes of sporadic origin. The aim of this study was to define a robust and inexpensive strategy for such classification in clinical practice.
  
  
  METHODS
  Tumours and blood samples from 262 successive patients with colorectal adenocarcinomas were collected. Expression of the MMR proteins MLH1, MSH2, and MSH6 by immunohistochemistry (IHC) was compared with MSI DNA analysis. Methylation analysis of MLH1 and mutation analysis for BRAF V600E were compared in samples with MSI and/or lack of MLH1 expression to determine if the tumour was likely to be sporadic.
  
  
  RESULTS
  Thirty-nine (14.9%) of the tumours showed MMR deficiency by IHC or by microsatellite analysis. Sporadic inactivation by methylation of MLH1 promoter was found in 35 patients whereby the BRAF activating V600E mutation, indicating sporadic origin, was found in 32 tumours. On the basis of molecular characteristics we found 223 patients with intact MMR, 35 patients with sporadic MMR deficiency, and four patients who were likely to have hereditary MMR deficiency.
  
  
  CONCLUSIONS
  To obtain the maximal benefit for patients and clinicians, MMR testing should be supplemented with MLH1 methylation or BRAF mutation analysis to distinguish sporadic patients from likely hereditary ones. MMR deficient patients with sporadic disease can be reassured of the better prognosis and the likely hereditary cases should receive genetic counselling.
authors.affiliation: Danish Colorectal Cancer Group South, University of Southern Denmark and Vejle Hospital, Vejle, Denmark. laheje@vgs.vejleamt.dk
authors.forename: L H
authors.initials: LH
authors.lastname: Jensen
authors.forename: J
authors.initials: J
authors.lastname: Lindebjerg
authors.forename: L
authors.initials: L
authors.lastname: Byriel
authors.forename: S
authors.initials: S
authors.lastname: Kolvraa
authors.forename: D G
authors.initials: DG
authors.lastname: Crüger
mesh_terms: D000230:Adenocarcinoma / Q000145:classification* / Q000235:genetics*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015179:Colorectal Neoplasms / Q000145:classification* / Q000235:genetics*; D019175:DNA Methylation; D053843:DNA Mismatch Repair; D004268:DNA-Binding Proteins / Q000032:analysis; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D051718:MutS Homolog 2 Protein / Q000032:analysis; D000074081:MutS Homolog 3 Protein; D009154:Mutation
chemical_list: D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C078444:MSH3 protein, human; D000074081:MutS Homolog 3 Protein; C497172:MSH2 protein, human; D051718:MutS Homolog 2 Protein