Journal of the National Cancer Institute Advance Access originally published online on September 14, 2009
JNCI Journal of the National Cancer Institute 2009 101(20):1423-1427; doi:10.1093/jnci/djp309
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© The Author 2009. Published by Oxford University Press.
BRIEF COMMUNICATION |
Polyclonality of BRAF Mutations in Acquired Melanocytic Nevi
Affiliations of authors: Department of Dermatology, Shinshu University School of Medicine, Matsumoto, Japan (JL, MT, HM, YG, KK, TS); Department of Surgery, Department of Immunology, and Department of Pathology, University of Pittsburgh Cancer Institute, Pittsburgh, PA (SF)
Correspondence to: Minoru Takata, MD, Department of Dermatology, Shinshu University School of Medicine, Asahi 3-1-1, Matsumoto 390-8621, Japan (e-mail:mtakata{at}shinshu-u.ac.jp).
Melanocytic nevi are thought to be senescent clones of melanocytes that have acquired an oncogenic BRAF mutation. BRAF mutation is considered to be a crucial step in the initiation of melanocyte transformation. However, using immunomagnetic separation or laser-capture microdissection, we examined BRAF mutations in sets of approximately 50 single cells isolated from acquired melanocytic nevi from 13 patients and found a substantial number of nevus cells that contained wild-type BRAF mixed with nevus cells that contained BRAFV600E. Furthermore, we simultaneously amplified BRAF exon 15 and a neighboring single nucleotide polymorphism (SNP), rs7801086, from nevus cell samples obtained from four patients who were heterozygous for this SNP. Subcloning and sequencing of the polymerase chain reaction products showed that both SNP alleles harbored the BRAFV600E mutation, indicating that the same BRAFV600E mutation originated from different cells. The polyclonality of BRAF mutations in acquired melanocytic nevi suggests that mutation of BRAF may not be an initial event in melanocyte transformation.
| CONTEXT AND CAVEATS Prior knowledge Oncogenic BRAF mutation has been considered to be an early step in the formation of melanocytic nevi, but recently, clonal heterogeneity was found in a few nevi. Study design Approximately 50 single cells were separated from each of 13 melanocytic nevi either by using immunomagnetic beads or by laser-capture microdissection and were subjected to single-cell polymerase chain reaction and sequencing to determine BRAF mutations. In another experiment, BRAF and a neighboring single-nucleotide polymorphism were simultaneously amplified from nevi of four patients who were heterozygous for the polymorphism. Contribution Although BRAF mutations were always found among nevus cells, cells that contained only wild-type BRAF predominated in nine of 13 nevi. When BRAF was sequenced from both alleles of four patients heterozygous for an adjacent polymorphism, both alleles harbored BRAF mutations. Implications These results suggest that BRAF may be mutated as a late event in melanocytic tumorigenesis. Limitations A small number of nevi of only two histological types were examined. From the Editors
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Manuscript received November 4, 2008; revised July 21, 2009; accepted August 10, 2009.
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J Natl Cancer Inst 2009 101: 1365.