IMPLICATIONS FOR PRACTICE: Hairy cell leukemia (HCL) has effective treatments including purine analogs with and without rituximab, and oral inhibitors of BRAF, MEK and Bruton's tyrosine kinase (BTK).
Identification of the BRAF-V600E kinase mutation as the genetic cause of HCL has opened the way, in the relapsed/refractory experimental setting, to targeted and non-myelotoxic effective strategies that are based on inhibition of BRAF with vemurafenib, co-inhibition of BRAF and its target MEK with dabrafenib and trametinib, and BRAF inhibition with vemurafenib combined with anti-CD20 immunotherapy.
Expert opinion: Ongoing and planned studies will help to optimize the use of BRAF inhibitor therapy for HCL by determining the efficacy of BRAF inhibition in combination with other antigen targeted or molecularly targeted therapies, and more broadly, to determine how hematologists can best utilize and sequence emerging diagnostic and therapeutic modalities in the care of patients with newly diagnosed and relapsed or refractory HCL.
Many such genetic events have already demonstrated clinical utility, such as BRAFV600E that confers sensitivity to vemurafenib in patients with hairy cell leukemia.
Hairy cell leukemia (HCL) is a rare, low-grade mature B-cell neoplasm with a characteristic clinical, morphological, immunophenotypic, and more recently described molecular (BRAFp.V600E mutation) profile.
In order to investigate the suitability of MinION sequencing on formalin-fixed paraffin-embedded samples, the presence and frequency of BRAF c.1799T > A mutation was investigated in two archival tissue specimens of Hairy cell leukemia and Hairy cell leukemia Variant.
The recent application of high-throughput sequencing to NHL not only advances the understanding of disease pathogenesis and classification, but allows the discovery of new drug targets, such as BRAF gene inhibition in hairy cell leukemia.
Diagnosis of HCL is based on morphological evidence of hairy cells, an HCL immunologic score of 3 or 4 based on the CD11C, CD103, CD123, and CD25 expression, the trephine biopsy which makes it possible to specify the degree of tumoral medullary infiltration and the presence of BRAFV600E somatic mutation.
As mutant BRAF alone is insufficient to drive malignant transformation in other histological cancers, it suggests that individual tumours utilise largely differing patterns of genetic somatic mutations to coalesce with BRAF V(600)E to drive pathogenesis of malignant HCLc disease.
Sensitive molecular assays for detecting BRAFV600E allow HCL (highly responsive to purine analogs) to be better distinguished from HCL-like disorders, which are treated differently.
The recent surge in next generation sequencing (NGS) technology has shed more light on the genetic landscape of SBCLs through characterization of numerous driver mutations including SF3B1 and NOTCH1 in CLL, ATM and CCND1 in MCL, KMT2D and EPHA7 in FL, MYD88 (L265P) in LPL, KLF2 and NOTCH2 in splenic MZL (SMZL) and BRAF (V600E) in HCL.
In this issue of Blood, Pettirossi et al, including Drs Tiacci and Falini, who led the effort in 2011 defining the BRAF-V600E driving mutation in hairy cell leukemia (HCL),provide extensive laboratory studies showing that inhibitors of BRAF-V600E and/or mitogen-activated protein kinase kinase (MEK) reach their targets and cause HCL cell death
The discovery of the BRAFV600E mutation in most cases of classical hairy cell leukemia opens up unique opportunities for tumor specific treatment of HCL targeting the MEK/ERK signaling pathway.
We assessed the safety and activity of the oral BRAF inhibitor vemurafenib in patients with hairy-cell leukemia that had relapsed after treatment with a purine analogue or who had disease that was refractory to purine analogues.
Modern approaches to the evaluation and treatment of HCL include detailed molecular analysis which informs therapeutic options, which may consist of traditional therapies such as purine nucleoside analogs, or targeted therapies with antibodies, BTK inhibitors, or BRAF inhibitors, or combination therapy.