BRAF Mutations in Hairy-Cell Leukemia — NEJM

Original Article

BRAF Mutations in Hairy-Cell Leukemia
Enrico Tiacci, M.D., Vladimir Trifonov, Ph.D., Gianluca Schiavoni, Ph.D., Antony Holmes, Ph.D., Wolfgang Kern, M.D., Maria Paola Martelli, M.D., Alessandra Pucciarini, Ph.D., Barbara Bigerna, B.Sc., Roberta Pacini, B.Sc., Victoria A. Wells, B.Sc., Paolo Sportoletti, M.D., Valentina Pettirossi, Ph.D., Roberta Mannucci, Ph.D., Oliver Elliott, M.Sc., Arcangelo Liso, M.D., Achille Ambrosetti, M.D., Alessandro Pulsoni, M.D., Francesco Forconi, M.D., Livio Trentin, M.D., Gianpietro Semenzato, M.D., Giorgio Inghirami, M.D., Monia Capponi, M.D., Francesco Di Raimondo, M.D., Caterina Patti, M.D., Luca Arcaini, M.D., Pellegrino Musto, M.D., Stefano Pileri, M.D., Claudia Haferlach, M.D., Susanne Schnittger, Ph.D., Giovanni Pizzolo, M.D., Robin Foà, M.D., Laurent Farinelli, Ph.D., Torsten Haferlach, M.D., Laura Pasqualucci, M.D., Raul Rabadan, Ph.D., and Brunangelo Falini, M.D.

N Engl J Med 2011; 364:2305-2315June 16, 2011

Abstract
Background
Hairy-cell leukemia (HCL) is a well-defined clinicopathological entity whose underlying genetic lesion is still obscure.


Methods
We searched for HCL-associated mutations by performing massively parallel sequencing of the whole exome of leukemic and matched normal cells purified from the peripheral blood of an index patient with HCL. Findings were validated by Sanger sequencing in 47 additional patients with HCL.


Results
Whole-exome sequencing identified five missense somatic clonal mutations that were confirmed on Sanger sequencing, including a heterozygous mutation in BRAF that results in the BRAF V600E variant protein. Since BRAF V600E is oncogenic in other tumors, further analyses were focused on this genetic lesion. The same BRAF mutation was noted in all the other 47 patients with HCL who were evaluated by means of Sanger sequencing. None of the 195 patients with other peripheral B-cell lymphomas or leukemias who were evaluated carried the BRAF V600E variant, including 38 patients with splenic marginal-zone lymphomas or unclassifiable splenic lymphomas or leukemias. In immunohistologic and Western blot studies, HCL cells expressed phosphorylated MEK and ERK (the downstream targets of the BRAF kinase), indicating a constitutive activation of the RAF–MEK–ERK mitogen-activated protein kinase pathway in HCL. In vitro incubation of BRAF-mutated primary leukemic hairy cells from 5 patients with PLX-4720, a specific inhibitor of active BRAF, led to a marked decrease in phosphorylated ERK and MEK.


Conclusions
The BRAF V600E mutation was present in all patients with HCL who were evaluated. This finding may have implications for the pathogenesis, diagnosis, and targeted therapy of HCL. (Funded by Associazione Italiana per la Ricerca sul Cancro and others.)

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BRAF Mutations in Hairy-Cell Leukemia — NEJM