title: Polyclonality of BRAF mutations in primary melanoma and the selection of mutant alleles during progression.
abstract: BACKGROUND
  Oncogenic BRAF mutation had been considered to be a founder event in the formation of melanocytic tumours; however, we recently argued against this notion by showing marked polyclonality of BRAF mutations in acquired melanocytic nevi (Lin et al, J Natl Cancer Inst., 2009; 101:1423-7). Here, we tested whether similar heterogeneity of BRAF mutations exists in primary melanomas.
  
  
  METHODS
  We isolated and sequenced single melanoma cells from five primary melanoma tissues using antibodies against human high-molecular-weight melanoma-associated antigen. We also examined 10 primary melanomas by the sensitive Mutector assay detecting the BRAF(V600E) mutation, as well as by cloning and sequencing of separated alleles. Furthermore, we estimated the frequency of BRAF mutant alleles in paired samples of primary tumour and recurrence or metastasis in three patients.
  
  
  RESULTS
  Single-cell mutation analyses revealed that four of five primary melanomas contained both BRAF-wild-type and BRAF-mutant tumour cells. Tumour heterogeneity in terms of BRAF mutations was also shown in 8 of 10 primary melanomas. Selection of BRAF mutant alleles during progression was demonstrated in all the three patients.
  
  
  CONCLUSIONS
  Acquisition of a BRAF mutation is not a founder event, but may be one of the multiple clonal events in melanoma development, which is selected for during the progression.
authors.affiliation: Department of Dermatology, Shinshu University School of Medicine, Matsumoto, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Lin
authors.forename: Y
authors.initials: Y
authors.lastname: Goto
authors.forename: H
authors.initials: H
authors.lastname: Murata
authors.forename: K
authors.initials: K
authors.lastname: Sakaizawa
authors.forename: A
authors.initials: A
authors.lastname: Uchiyama
authors.forename: T
authors.initials: T
authors.lastname: Saida
authors.forename: M
authors.initials: M
authors.lastname: Takata
mesh_terms: D000483:Alleles; D045744:Cell Line, Tumor; D002999:Clone Cells; D006801:Humans; D008545:Melanoma / Q000235:genetics; D009154:Mutation; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D012878:Skin Neoplasms / Q000235:genetics
chemical_list: C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf