title: Systematic review: brain metastases from colorectal cancer--Incidence and patient characteristics.
abstract: BACKGROUND
  Brain metastases (BM) from colorectal cancer (CRC) are a rare event. However, the implications for affected patients are severe, and the incidence has been reported to be increasing. For clinicians, knowledge about the characteristics associated with BM is important and could lead to earlier diagnosis and improved survival.
  
  
  METHODS
  In this paper, we describe the incidence as well as characteristics associated with BM based on a systematic review of the current literature, following the PRISMA guidelines.
  
  
  RESULTS
  We show that the incidence of BM in CRC patients ranges from 0.6 to 3.2%. BM are a late stage phenomenon, and young age, rectal primary and lung metastases are associated with increased risk of developing BM. Molecular markers such as KRAS, BRAF, NRAS mutation as well as an increase in CEA and CA19.9 levels are suggested predictors of brain involvement. However, only KRAS mutations are reasonably well investigated and associated with an increased risk of BM.
  
  
  CONCLUSIONS
  The incidence of BM from CRC is 0.6 to 3.2% and did not seem to increase over time. Development of BM is associated with young age, lung metastases, rectal primary and KRAS mutation. Increased awareness of brain involvement in patients with these characteristics is necessary.
authors.affiliation: Department of Oncology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730, Herlev, Denmark. troels.dreier.christensen.01@regionh.dk.
authors.forename: Troels Dreier
authors.initials: TD
authors.lastname: Christensen
authors.affiliation: Department of Oncology, Aarhus University Hospital, Nørrebrogade 44, DK-8000, Aarhus C, Denmark.
authors.forename: Karen-Lise Garm
authors.initials: KL
authors.lastname: Spindler
authors.affiliation: Department of Oncology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730, Herlev, Denmark.
authors.forename: Jesper Andreas
authors.initials: JA
authors.lastname: Palshof
authors.affiliation: Department of Oncology, Herlev Hospital, University of Copenhagen, Herlev Ringvej 75, DK-2730, Herlev, Denmark.
authors.forename: Dorte Lisbet
authors.initials: DL
authors.lastname: Nielsen
mesh_terms: D000367:Age Factors; D001932:Brain Neoplasms / Q000235:genetics* / Q000473:pathology / Q000556:secondary; D015179:Colorectal Neoplasms / Q000235:genetics* / Q000473:pathology; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics; D056726:Genetic Association Studies; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology / Q000556:secondary; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation; D011379:Prognosis; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D016283:Proto-Oncogene Proteins p21(ras) / Q000235:genetics*; D012307:Risk Factors
chemical_list: C117307:KRAS protein, human; D008565:Membrane Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020558:GTP Phosphohydrolases; C579846:NRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)
keywords: Brain metastases; Colorectal cancer; Incidence; Lung metastases; RAS mutations