title: Microsatellite instability has a positive prognostic impact on stage II colorectal cancer after complete resection: results from a large, consecutive Norwegian series.
abstract: BACKGROUND
  Microsatellite instability (MSI) was suggested as a marker for good prognosis in colorectal cancer in 1993 and a systematic review from 2005 and a meta-analysis from 2010 support the initial observation. We here assess the prognostic impact and prevalence of MSI in different stages in a consecutive, population-based series from a single hospital in Oslo, Norway.
  
  
  METHODS
  Of 1274 patients, 952 underwent major resection of which 805 were included in analyses of MSI prevalence and 613 with complete resection in analyses of outcome. Formalin-fixed tumor tissue was used for PCR-based MSI analyses.
  
  
  RESULTS
  The overall prevalence of MSI was 14%, highest in females (19%) and in proximal colon cancer (29%). Five-year relapse-free survival (5-year RFS) was 67% and 55% (P = 0.030) in patients with MSI and MSS tumors, respectively, with the hazard ratio (HR) equal to 1.60 (P = 0.045) in multivariate analysis. The improved outcome was confined to stage II patients who had 5-year RFS of 74% and 56% respectively (P = 0.010), HR = 2.02 (P = 0.040). Examination of 12 or more lymph nodes was significantly associated with proximal tumor location (P < 0.001).
  
  
  CONCLUSIONS
  MSI has an independent positive prognostic impact on stage II colorectal cancer patients after complete resection.
authors.affiliation: Department of Gastrointestinal Surgery, Oslo University Hospital-Aker, Oslo, Norway.
authors.forename: M A
authors.initials: MA
authors.lastname: Merok
authors.forename: T
authors.initials: T
authors.lastname: Ahlquist
authors.forename: E C
authors.initials: EC
authors.lastname: Røyrvik
authors.forename: K F
authors.initials: KF
authors.lastname: Tufteland
authors.forename: M
authors.initials: M
authors.lastname: Hektoen
authors.forename: O H
authors.initials: OH
authors.lastname: Sjo
authors.forename: T
authors.initials: T
authors.lastname: Mala
authors.forename: A
authors.initials: A
authors.lastname: Svindland
authors.forename: R A
authors.initials: RA
authors.lastname: Lothe
authors.forename: A
authors.initials: A
authors.lastname: Nesbakken
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000235:genetics; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000401:mortality / Q000601:surgery*; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008198:Lymph Nodes / Q000473:pathology; D008207:Lymphatic Metastasis; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local / Q000235:genetics*; D009367:Neoplasm Staging; D009664:Norway; D011379:Prognosis
chemical_list: D014408:Biomarkers, Tumor