Killing two birds with one stone: BRAF V600E inhibitor therapy for hairy cell leukemia and Langerhans/dendritic cell sarcoma
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We read with great interest the article published in Annals of Hematology on a patient with Langerhans/dendritic cell sarcoma arising from hairy cell leukemia with both lesions demonstrating almost identical karyotypes and identical clonal immunoglobulin gene rearrangements . This case is very interesting in light of fresh data on BRAF V600E mutations in several different tumor types .
Whole exome sequencing of patients with hairy cell leukemia has revealed BRAF V600E mutation . This BRAFV600E mutation has been described as a disease-defining event  in hairy cell leukemia and has been implicated in the pathogenesis of hairy cell leukemia. Langerhans cell histiocytoses have also been reported to harbor the BRAFV600E mutation . Histiocytoses are extremely rare diseases with variable clinical syndromes and BRAFV600E mutations have been reported in multiple histiocytoses subtypes including Erdheim–Chester disease .
In the light of these results, the case reported is very fascinating . It may be interesting to profile the BRAFV600E status of the hairy cell leukemic clone and the histiocytic/dendritic sarcoma clone. If confirmed, this could suggest clonality and may also indicate a common origin of these diverse rare diseases. Moreover, for this particular patient this may have implications for targeted therapy. Vemurafenib, a BRAF inhibitor has been recently Food and Drug Administration approved for the therapy of BRAFV600E mutant metastatic melanoma . Although hairy cell leukemia is a treatable disease with standard regimens, rare relapsed patients could still benefit from BRAF inhibitor targeted therapy and a proof of concept study has already been reported . Some patients with Langerhans cell histocytoses may have an aggressive clinical course and patients with refractory disease may have few options. BRAF inhibitor-targeted therapy may be the way to kill two birds with one stone such as in this patient if BRAFV600E mutation is confirmed.
Conflict of interest
The authors declare that they have no conflict of interest