Recurrent CDKN1B (p27) mutations in hairy cell leukemia

MEN4 and CDKN1B mutations: the latest of the MEN syndromes

Multiple endocrine neoplasia (MEN) refers to a group of autosomal dominant disorders with generally high penetrance that lead to the development of a wide spectrum of endocrine and non-endocrine manifestations. The most frequent among these conditions is MEN type 1 (MEN1), which is caused by germline heterozygous loss-of-function mutations in the tumor suppressor gene MEN1 MEN1 is characterized by primary hyperparathyroidism (PHPT) and functional or nonfunctional pancreatic neuroendocrine tumors and pituitary adenomas. Approximately 10% of patients with familial or sporadic MEN1-like phenotype do not have MEN1 mutations or deletions. A novel MEN syndrome was discovered, initially in rats (MENX), and later in humans (MEN4), which is caused by germline mutations in the putative tumor suppressor CDKN1B The most common phenotype of the 19 established cases of MEN4 that have been described to date is PHPT followed by pituitary adenomas. Recently, somatic or germline mutations in CDKN1B were also identified in patients with sporadic PHPT, small intestinal neuroendocrine tumors, lymphoma and breast cancer, demonstrating a novel role for CDKN1B as a tumor susceptibility gene for other neoplasms. In this review, we report on the genetic characterization and clinical features of MEN4.

Genomic analysis of hairy cell leukemia identifies novel recurrent genetic alterations

Classical hairy cell leukemia (cHCL) is characterized by a near 100% frequency of the BRAFV600E mutation, whereas ∼30% of variant HCLs (vHCLs) have MAP2K1 mutations. However, recurrent genetic alterations cooperating with BRAFV600E or MAP2K1 mutations in HCL, as well as those in MAP2K1 wild-type vHCL, are not well defined. We therefore performed deep targeted mutational and copy number analysis of cHCL (n = 53) and vHCL (n = 8). The most common genetic alteration in cHCL apart from BRAFV600E was heterozygous loss of chromosome 7q, the minimally deleted region of which targeted wild-type BRAF, subdividing cHCL into those hemizygous versus heterozygous for the BRAFV600E mutation. In addition to CDKN1B mutations in cHCL, recurrent inactivating mutations in KMT2C (MLL3) were identified in 15% and 25% of cHCLs and vHCLs, respectively. Moreover, 13% of vHCLs harbored predicted activating mutations in CCND3 A change-of-function mutation in the splicing factor U2AF1 was also present in 13% of vHCLs. Genomic analysis of de novo vemurafenib-resistant cHCL identified a novel gain-of-function mutation in IRS1 and losses of NF1 and NF2, each of which contributed to resistance. These data provide further insight into the genetic bases of cHCL and vHCL and mechanisms of RAF inhibitor resistance encountered clinically.

Diagnosis and classification of hematologic malignancies on the basis of genetics

Genomic analysis has greatly influenced the diagnosis and clinical management of patients affected by diverse forms of hematologic malignancies. Here, we review how genetic alterations define subclasses of patients with acute leukemias, myelodysplastic syndromes (MDS), myeloproliferative neoplasms (MPNs), non-Hodgkin lymphomas, and classical Hodgkin lymphoma. These include new subtypes of acute myeloid leukemia defined by mutations in RUNX1 or BCR-ABL1 translocations as well as a constellation of somatic structural DNA alterations in acute lymphoblastic leukemia. Among patients with MDS, detection of mutations in SF3B1 define a subgroup of patients with the ring sideroblast form of MDS and a favorable prognosis. For patients with MPNs, detection of the BCR-ABL1 fusion delineates chronic myeloid leukemia from classic BCR-ABL1^- MPNs, which are largely defined by mutations in JAK2, CALR, or MPL In the B-cell lymphomas, detection of characteristic rearrangements involving MYC in Burkitt lymphoma, BCL2 in follicular lymphoma, and MYC/BCL2/BCL6 in high-grade B-cell lymphomas are essential for diagnosis. In T-cell lymphomas, anaplastic large-cell lymphoma is defined by mutually exclusive rearrangements of ALK, DUSP22/IRF4, and TP63 Genetic alterations affecting TP53 and the mutational status of the immunoglobulin heavy-chain variable region are important in clinical management of chronic lymphocytic leukemia. Additionally, detection of BRAFV600E mutations is helpful in the diagnosis of classical hairy cell leukemia and a number of histiocytic neoplasms. Numerous additional examples provided here demonstrate how clinical evaluation of genomic alterations have refined classification of myeloid neoplasms and major forms of lymphomas arising from B, T, or natural killer cells.

Genomics of Hairy Cell Leukemia

Hairy cell leukemia (HCL) is a chronic mature B-cell neoplasm with unique clinicopathologic features and an initial exquisite sensitivity to chemotherapy with purine analogs; however, the disease relapses, often repeatedly. The enigmatic pathogenesis of HCL was recently clarified by the discovery of its underlying genetic cause, the BRAF-V600E kinase-activating mutation, which is somatically and clonally present in almost all patients through the entire disease spectrum and clinical course. By aberrantly activating the RAF-MEK-ERK signaling pathway, BRAF-V600E shapes key biologic features of HCL, including its specific expression signature, hairy morphology, and antiapoptotic behavior. Accompanying mutations of the KLF2 transcription factor or the CDKN1B/p27 cell cycle inhibitor are recurrent in 16% of patients with HCL and likely cooperate with BRAF-V600E in HCL pathogenesis. Conversely, BRAF-V600E is absent in other B-cell neoplasms, including mimickers of HCL that require different treatments (eg, HCL-variant and splenic marginal zone lymphoma). Thus, testing for BRAF-V600E allows for a genetics-based differential diagnosis between HCL and HCL-like tumors, even noninvasively in routine blood samples. BRAF-V600E also represents a new therapeutic target. Patients' leukemic cells exposed ex vivo to BRAF inhibitors are spoiled of their HCL identity and then undergo apoptosis. In clinical trials of patients with HCL who have experienced multiple relapses after purine analogs or who are refractory to purine analogs, a short course of the oral BRAF inhibitor vemurafenib produced an almost 100% response rate, including complete remission rates of 35% to 42%, without myelotoxicity. To further improve on these results, it will be important to clarify the mechanisms of incomplete leukemic cell eradication by vemurafenib and to explore chemotherapy-free combinations of a BRAF inhibitor with other targeted agents (eg, a MEK inhibitor and/or an anti-CD20 monoclonal antibody).

Loss of p27 expression is associated with MEN1 gene mutations in sporadic parathyroid adenomas

MEN1 is the main gene responsible for tumorigenesis of syndromic and sporadic primary hyperparathyroidism (PHPT). Germline mutations of the CDKN1B/p27^Kip gene have been associated with multiple endocrine tumors in rats and humans. To evaluate the involvement of the CDKN1B gene and its relationship with MEN1 in sporadic PHPT, we carried out sequencing and loss of heterozygosity analyses of the CDKN1B gene in 147 sporadic parathyroid adenomas. p27 immunohistochemistry and genetic screening of the MEN1 gene were performed in 50 cases. Three germline CDKN1B variants (c.-80C>T, c.-29_-26delAGAG, c.397C>A) were identified in 3/147 patients. Reduction of CDKN1B gene transcription rate was demonstrated in vitro for the novel c.-80C>T and the c.-29_-26delAGAG variants. Loss of p27 expression was detected in the tumor carrying the c.-29_-26delAGAG variant. Two tumors carrying the CDKN1B variants also harbored a MEN1 mutation. Fifty-four percent of 50 CDKN1B mutation-negative tumors had a reduction of p27 nuclear staining. Somatic MEN1 mutations, identified in 15/50 samples, significantly segregated in tumors negative for nuclear and cytoplasmic p27 staining. The germline nature of the CDKN1B mutations suggests that they might predispose to PHPT. The lack of somatic CDKN1B mutations in our samples points to a rare involvement in parathyroid adenomas, despite the frequent loss of nuclear p27 expression. MEN1 biallelic inactivation seems to be directly related to down-regulation of p27 expression through the inhibition of CDKN1B gene transcription.

BRAF V600E mutation in hairy cell leukemia: from bench to bedside

Hairy cell leukemia (HCL) is a distinct clinicopathological entity whose underlying genetic lesion has remained a mystery for over half a century. The BRAF V600E mutation is now recognized as the causal genetic event of HCL because it is somatic, present in the entire tumor clone, detectable in almost all cases at diagnosis (encompassing the whole disease spectrum), and stable at relapse. BRAF V600E leads to the constitutive activation of the RAF-MEK-extracellular signal-regulated kinase (ERK) signaling pathway which represents the key event in the molecular pathogenesis of HCL. KLF2 and CDNK1B (p27) mutations may cooperate with BRAF V600E in promoting leukemic transformation. Sensitive molecular assays for detecting BRAF V600E allow HCL (highly responsive to purine analogs) to be better distinguished from HCL-like disorders, which are treated differently. In vitro preclinical studies on purified HCL cells proved that BRAF and MEK inhibitors can induce marked dephosphorylation of MEK/ERK, silencing of RAF-MEK-ERK pathway transcriptional output, loss of the HCL-specific gene expression profile signature, change of morphology from “hairy” to “smooth,” and eventually apoptosis. The overall response rate of refractory/relapsed HCL patients to the BRAF inhibitor vemurafenib approached 100%, with 35% to 40% complete remissions (CRs). The median relapse free-survival was about 19 months in patients who had achieved CR and 6 months in those who had obtained a partial response. Future therapeutic perspectives include: (1) combining BRAF inhibitors with MEK inhibitors or immunotherapy (anti-CD20 monoclonal antibody) to increase the percentage of CRs and (2) better understanding of the molecular mechanisms underlying resistance of HCL cells to BRAF inhibitors.

Molecular Pathology: Predictive, Prognostic, and Diagnostic Markers in Lymphoid Neoplasms

Lymphoid neoplasms show great diversity in morphology, immunophenotypic profile, and postulated cells of origin, which also reflects the variety of genetic alterations within this group of tumors. This review discusses many of the currently known genetic alterations in selected mature B-cell and T-cell lymphoid neoplasms, and their significance as diagnostic, prognostic, and therapeutic markers. Given the rapidly increasing number of genetic alterations that have been described in this group of tumors, and that the clinical significance of many is still being studied, this is not an entirely exhaustive review of all of the genetic alterations that have been reported.

Effects of valproic acid and pioglitazone on cell cycle progression and proliferation of T-cell acute lymphoblastic leukemia Jurkat cells

OBJECTIVES

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignant tumor. Administration of chemical compounds influencing apoptosis and T cell development has been discussed as promising novel therapeutic strategies. Valproic acid (VPA) as a recently emerged anti-neoplastic histone deacetylase (HDAC) inhibitor and pioglitazone (PGZ) as a high-affinity peroxisome proliferator-activated receptor-gamma (PPARγ) agonist have been shown to induce apoptosis and cell cycle arrest in different studies. Here, we aimed to investigate the underlying molecular mechanisms involved in anti-proliferative effects of these compounds on human Jurkat cells.

MATERIALS AND METHODS

Treated cells were evaluated for cell cycle progression and apoptosis using flowcytometry and MTT viability assay. Real-time RT-PCR was carried out to measure the alterations in key genes associated with cell death and cell cycle arrest.

RESULTS

Our findings illustrated that both VPA and PGZ can inhibit Jurkat E6.1 cells in vitro after 24 hr; however, PGZ 400 μM presents the most anti-proliferative effect. Interestingly, treated cells have been arrested in G2/M with deregulated cell division cycle 25A (Cdc25A) phosphatase and cyclin-dependent kinase inhibitor 1B (CDKN1B or p27) expression. Expression of cyclin D1 gene was inhibited when DNA synthesis entry was declined. Cell cycle deregulation in PGZ and VPA-exposed cells generated an increase in the proportion of aneuploid cell population, which has not reported before.

CONCLUSION

These findings define that anti-proliferative effects of PGZ and VPA on Jurkat cell line are mediated by cell cycle deregulation. Thus, we suggest PGZ and VPA may relieve potential therapeutic application against apoptosis-resistant malignancies.

p27(KIP1) and PTEN cooperate in myeloproliferative neoplasm tumor suppression in mice

PTEN acts as a phosphatase for PIP3 and negatively regulates the PI3K/AKT pathway, and p27^KIP1 is a cyclin-dependent kinase inhibitor that regulates the G1 to S-phase transition by binding to and regulating the activity of cyclin-dependent kinases. Genetic alterations of PTEN or CDKN1B (p27^KIP1) are common in hematological malignancies. To better understand how mutations in these two genes might cooperate in leukemogenesis, we inactivated both genes in the hematological compartment in mice. Here, we show that the combined inactivation of Pten and Cdkn1b results in a more severe myeloproliferative neoplasm phenotype associated with lower hemoglobin, enlarged spleen and liver, and shorter lifespan compared to inactivation of Pten alone. More severe anemia and increased myeloid infiltration and destruction of the spleen contributed to the earlier death of these mice, and elevated p-AKT, cyclin D1, and cyclin D3 might contribute to the development of this phenotype. In conclusion, PTEN and p27^KIP1 cooperate in tumor suppression in the hematological compartment.

Treatment outcomes and secondary cancer incidence in young patients with hairy cell leukaemia

Repeated therapy of hairy cell leukaemia (HCL) with treatments that have potential long-term toxicities has raised concerns regarding increased risk for younger patients. We compared clinical outcomes and disease complications in 63 patients with HCL aged ≤40 years at diagnosis with 268 patients >40 years treated at Memorial Sloan Kettering Cancer Center. The rate of complete remission following initial therapy was 87% and 83% (P = 0·71) and estimated 10-year overall survival was 100% and 82% (P = 0·25) in younger and older patients, respectively. Younger patients required therapy earlier and had a significantly shorter time between first and second therapy (median: 63 months vs. 145 months) (P = 0·008). Younger patients required significantly more lines of therapy during follow-up. The 10-year cumulative incidence of secondary malignancies in young and old patients was 0·205 and 0·287, respectively (P = 0·22). The incidence of secondary cancers in patients aged >40 years at diagnosis increased with the number of treatments for HCL (P = 0·018). These results highlight that young patients with HCL have shorter responses to treatment and require more lines of therapy to maintain disease control, while attaining similar long-term survival. This has implications in the design of future clinical trials given our findings that secondary malignancies increase with more chemotherapy exposure.

CD5 positive hairy cell leukemia: A rare case report with brief review of literature

OBJECTIVE

The aberrant expression of CD5 in both HCL and HCL-v is a very rare event. Although a number of CD5 positive HCL and HCL-v cases have been reported, but these are far and few in between. We aimed to review the reported cases of CD5 positive HCL and its variant.

METHOD

We hereby report a case of CD5 positive HCL, with variations in PIK3CA and PDGFRA gene, along with a brief review of literature of the cases of CD5 positive HCL and its variant.

RESULTS AND CONCLUSION

The current case was positive for CD103, CD11c, CD25, and CD123 which has led the diagnosis to be of typical HCL. With the extensive literature review we found that only 26 cases of hairy cell leukemia [HCL and HCL-v] bearing CD5 expression have been reported so far. The positivity of CD5 is more common in HCL-v as compared to HCL. Additional prospective studies of CD5+ HCL and its variants are required to show whether they are a clinically significant subgroup of lymphoid malignancies. © 2016 International Clinical Cytometry Society.

Genetic aberrations in small B-cell lymphomas and leukemias: molecular pathology, clinical relevance and therapeutic targets

Small B-cell lymphomas and leukemias (SBCLs) are a clinically, morphologically, immunophenotypically and genetically heterogeneous group of clonal lymphoid neoplasms, including entities such as chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL), mantle cell lymphoma (MCL), follicular lymphoma (FL), lymphoplasmacytic lymphoma (LPL), marginal zone lymphoma (MZL) and hairy cell leukemia (HCL). The pathogenesis of some of these lymphoid malignancies is characterized by distinct translocations, for example t(11;14) in the majority of cases of MCL and t(14;18) in most cases of FL, whereas other entities are associated with a variety of recurrent but nonspecific numeric chromosomal abnormalities, as exemplified by del(13q14), del(11q22), and +12 in CLL, and yet others such as LPL and HCL that lack recurrent or specific cytogenetic aberrations. 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. The identification of distinct genetic lesions not only provides greater insight into the molecular pathogenesis of these disorders but also identifies potential valuable biomarkers for prognostic stratification, as well as specific targets for directed therapy. This review discusses the well-established and recently identified molecular lesions underlying the pathogenesis of SBCLs, highlights their clinical relevance and summarizes novel targeted therapies.

The non-canonical functions of p27(Kip1) in normal and tumor biology

p27(Kip1) was first discovered as a key regulator of cell proliferation. The canonical function of p27(Kip1) is inhibition of cyclin-dependent kinase (CDK) activity. In addition to its initial identification as a CDK inhibitor, p27(Kip1) has also emerged as an intrinsically unstructured, multifunctional protein with numerous non-canonical, CDK-independent functions that exert influence on key processes such as cell cycle regulation, cytoskeletal dynamics and cellular plasticity, cell migration, and stem-cell proliferation and differentiation. Many of these non-canonical functions, depending on the cell-specific contexts such as oncogenic activation of signaling pathways, have the ability to turn pro-oncogenic in nature and even contribute to tumor-aggressiveness and metastasis. This review discusses the various non-canonical, CDK-independent mechanisms by which p27(Kip1) functions either as a tumor-suppressor or tumor-promoter.

Comprehensive mutational analysis of primary and relapse acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) is a subtype of myeloid leukemia characterized by differentiation block at the promyelocyte stage. Besides the presence of chromosomal rearrangement t(15;17), leading to the formation of PML-RARA (promyelocytic leukemia-retinoic acid receptor alpha) fusion, other genetic alterations have also been implicated in APL. Here, we performed comprehensive mutational analysis of primary and relapse APL to identify somatic alterations, which cooperate with PML-RARA in the pathogenesis of APL. We explored the mutational landscape using whole-exome (n=12) and subsequent targeted sequencing of 398 genes in 153 primary and 69 relapse APL. Both primary and relapse APL harbored an average of eight non-silent somatic mutations per exome. We observed recurrent alterations of FLT3, WT1, NRAS and KRAS in the newly diagnosed APL, whereas mutations in other genes commonly mutated in myeloid leukemia were rarely detected. The molecular signature of APL relapse was characterized by emergence of frequent mutations in PML and RARA genes. Our sequencing data also demonstrates incidence of loss-of-function mutations in previously unidentified genes, ARID1B and ARID1A, both of which encode for key components of the SWI/SNF complex. We show that knockdown of ARID1B in APL cell line, NB4, results in large-scale activation of gene expression and reduced in vitro differentiation potential.

BRAF inhibition in hairy cell leukemia with low-dose vemurafenib

The activating mutation of the BRAF serine/threonine protein kinase (BRAF V600E) is the key driver mutation in hairy cell leukemia (HCL), suggesting opportunities for therapeutic targeting. We analyzed the course of 21 HCL patients treated with vemurafenib outside of trials with individual dosing regimens (240-1920 mg/d; median treatment duration, 90 days). Vemurafenib treatment improved blood counts in all patients, with platelets, neutrophils, and hemoglobin recovering within 28, 43, and 55 days (median), respectively. Complete remission was achieved in 40% (6/15 of evaluable patients) and median event-free survival was 17 months. Response rate and kinetics of response were independent of vemurafenib dosing. Retreatment with vemurafenib led to similar response patterns (n = 6). Pharmacodynamic analysis of BRAF V600E downstream targets showed that vemurafenib (480 mg/d) completely abrogated extracellular signal-regulated kinase phosphorylation of hairy cells in vivo. Typical side effects also occurred at low dosing regimens. We observed the development of acute myeloid lymphoma (AML) subtype M6 in 1 patient, and the course suggested disease acceleration triggered by vemurafenib. The phosphatidylinositol 3-kinase hotspot mutation (E545K) was identified in the AML clone, providing a potential novel mechanism for paradoxical BRAF activation. These data provide proof of dependence of HCL on active BRAF signaling. We provide evidence that antitumor and side effects are observed with 480 mg vemurafenib, suggesting that dosing regimens in BRAF-driven cancers could warrant reassessment in trials with implications for cost of cancer care.

Exome Sequencing in Classic Hairy Cell Leukaemia Reveals Widespread Variation in Acquired Somatic Mutations between Individual Tumours Apart from the Signature BRAF V(600)E Lesion

In classic Hairy cell leukaemia (HCLc), a single case has thus far been interrogated by whole exome sequencing (WES) in a treatment naive patient, in which BRAF V(600)E was identified as an acquired somatic mutation and confirmed as occurring near-universally in this form of disease by conventional PCR-based cohort screens. It left open however the question whether other genome-wide mutations may also commonly occur at high frequency in presentation HCLc disease. To address this, we have carried out WES of 5 such typical HCLc cases, using highly purified splenic tumour cells paired with autologous T cells for germline. Apart from BRAF V(600)E, no other recurrent somatic mutation was identified in these HCLc exomes, thereby excluding additional acquired mutations as also prevalent at a near-universal frequency in this form of the disease. These data then place mutant BRAF at the centre of the neoplastic drive in HCLc. A comparison of our exome data with emerging genetic findings in HCL indicates that additional somatic mutations may however occur recurrently in smaller subsets of disease. 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.

Hairy Cell Leukemia Presenting with Isolated Skeletal Involvement Successfully Treated by Radiation Therapy and Cladribine: A Case Report and Review of the Literature

We describe an unusual case of hairy cell leukemia (HCL) in a 55-year-old male presenting with isolated skeletal disease as the initial manifestation without abnormal peripheral blood counts, bone marrow involvement, or splenomegaly. To the best of our knowledge, there have been only two previous reports of a similar case. The patient presented with pain in the right femur. Anteroposterior radiographs of both femurs revealed mixed lytic-sclerotic lesions. PET scan showed multiple metastatic lesions on axial skeleton, pelvis, and both femurs. Histopathological examination of the bone biopsy revealed an infiltrate of HCL. Localized radiation therapy to both proximal femurs and subsequently 4 weeks later, a 7-day course of 0.1 mg/kg/day cladribine provided complete remission with relief of symptoms and resolution of bone lesions. We addressed the manifestations and management of HCL patients with skeletal involvement.

Hairy cell leukemia: Past, present and future

This brief review highlights the sequence of therapeutic milestones and advances in our understanding of the biology of hairy cell leukemia (HCL) with a focus on recent molecular findings and how these may be applied to improve disease outcomes in the future. Targeted therapy is discussed in the context of the recently identified BRAF mutation and other genetic findings.

Genetic characterization of T-PLL reveals two major biologic subgroups and JAK3 mutations as prognostic marker

T-cell prolymphocytic leukemia (T-PLL) is a rare post-thymic T-cell neoplasm with aggressive clinical course and short overall survival. So far, due to the rareness of this disease, genetic data are available only from individual cases or small cohorts. In our study, we aimed at performing a comprehensive cytogenetic and molecular genetic characterization of T-PLL comprising the largest cohort of patients with T-PLL analyzed so far, including correlations between the respective markers and their impact on prognosis. Genetic abnormalities were found in all 51 cases with T-PLL, most frequently involving the TCRA/D locus (86%). Deletions were detected for ATM (69%) and TP53 (31%), whereas i(8)(q10) was observed in 61% of cases. Mutations in ATM, TP53, JAK1, and JAK3 were detected in 73, 14, 6, and 21% of patients, respectively. Additionally, BCOR mutations were observed for the first time in a lymphoid malignancy (8%). Two distinct genetic subgroups of T-PLL were identified: A large subset (86% of patients) showed abnormalities involving the TCRA/D locus activating the proto-oncogenes TCL1 or MTCP1, while the second group was characterized by a high frequency of TP53 mutations (4/7 cases). Further, analyses of overall survival identified JAK3 mutations as important prognostic marker, showing a significant negative impact.

BRAF inhibitor therapy in HCL

Targeted treatment approaches are transforming the therapeutic landscape of cancer care. The discovery of the BRAF V600E 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. The discovery and biological implications of BRAF V600E in HCL are summarized to form a basis for our current understanding of the potential for clinical exploitation. There is overwhelming clinical evidence for activity of inhibitors of BRAF in the disease. The review will review current trial activity as well as discuss novel trial concepts exploiting targeted treatment focusing on BRAF inhibition in HCL.

Recent advances in diagnosis and treatment of hairy cell leukemia

Hairy cell leukemia (HCL) is a rare, indolent B-cell lymphoproliferative disorder that accounts for 2% of all cases of leukemia. Most patients present with pancytopenia and splenomegaly with variable number of ‘hairy’ lymphocytes in blood. BRAF V600E mutation can be detected in virtually 100% of HCL cases and is absent in other B-cell lymphomas. The mutated gene and its responding abnormal protein can be used as specific markers in the diagnosis of HCL. New therapeutic modalities targeting on mutated BRAF and its downstream pathways have shown encouraging results in clinical trials. The objective of this review article is to discuss the recent developments in the diagnosis and management of hairy cell leukemia.