Incidence of the BRAF V600E mutation in chronic lymphocytic leukaemia and prolymphocytic leukaemia

Differential contribution for ERK1 and ERK2 kinases in BRAFV600E-triggered phenotypes in adult mouse models

The BRAF gene is mutated in a plethora of human cancers. The majority of such molecular lesions result in the expression of a constitutively active BRAF variant (BRAFV600E) which continuously bolsters cell proliferation. Although we recently addressed the early effects triggered by BRAFV600E-activation, the specific contribution of ERK1 and ERK2 in BRAFV600E-driven responses in vivo has never been explored. Here we describe the first murine model suitable for genetically dissecting the ERK1/ERK2 impact in multiple phenotypes induced by ubiquitous BRAFV600E-expression. We unveil that ERK1 is dispensable for BRAFV600E-dependent lifespan shortening and for BRAFV600E-driven tumor growth. We show that BRAFV600E-expression provokes an ERK1-independent lymphocyte depletion which does not rely on p21CIP1-induced cell cycle arrest and is unresponsive to ERK-chemical inhibition. Moreover, we also reveal that ERK1 is dispensable for BRAFV600E-triggered cytotoxicity in lungs and that ERK-chemical inhibition abrogates some of these detrimental effects, such as DNA damage, in Club cells but not in pulmonary lymphocytes. Our data suggest that ERK1/ERK2 contribution to BRAFV600E-driven phenotypes is dynamic and varies dependently on cell type, the biological function, and the level of ERK-pathway activation. Our findings also provide useful insights into the comprehension of BRAFV600E-driven malignancies pathophysiology as well as the consequences in vivo of novel ERK pathway-targeted anti-cancer therapies.

KRAS and RAS-MAPK Pathway Deregulation in Mature B Cell Lymphoproliferative Disorders

KRAS mutations account for the most frequent mutations in human cancers, and are generally correlated with disease aggressiveness, poor prognosis, and poor response to therapies. KRAS is required for adult hematopoiesis and plays a key role in B cell development and mature B cell proliferation and survival, proved to be critical for B cell receptor-induced ERK pathway activation. In mature B cell neoplasms, commonly seen in adults, KRAS and RAS-MAPK pathway aberrations occur in a relevant fraction of patients, reaching high recurrence in some specific subtypes like multiple myeloma and hairy cell leukemia. As inhibitors targeting the RAS-MAPK pathway are being developed and improved, it is of outmost importance to precisely identify all subgroups of patients that could potentially benefit from their use. Herein, we review the role of KRAS and RAS-MAPK signaling in malignant hematopoiesis, focusing on mature B cell lymphoproliferative disorders. We discuss KRAS and RAS-MAPK pathway aberrations describing type, incidence, mutual exclusion with other genetic abnormalities, and association with prognosis. We review the current therapeutic strategies applied in mature B cell neoplasms to counteract RAS-MAPK signaling in pre-clinical and clinical studies, including most promising combination therapies. We finally present an overview of genetically engineered mouse models bearing KRAS and RAS-MAPK pathway aberrations in the hematopoietic compartment, which are valuable tools in the understanding of cancer biology and etiology.

Biclonal lymphoproliferative disorders: another association with NOTCH1-mutated chronic lymphocytic leukaemias

INTRODUCTION

Biclonal lymphoid disorders, when two distinct lymphoproliferative disorders (LPD) co-exist, are rare (incidence of 1.4%) and associated with a poor prognosis. NOTCH1 mutations occur in 10% of CLL at diagnosis, associated with a short disease-free interval and increased risk of Richter's transformation. We hypothesised that the incidence of NOTCH1 mutations in CLL with a second LPD may be increased, because the mutation occurs early in leukaemogenesis, permitting clonal divergence.

METHODS

We identified 19 patients with biclonal LPD at diagnosis: 11 with CLL and a second LPD (group A) and 8 with a second distinct CLL (group B). NOTCH1 mutation analysis was performed and clinical outcome investigated.

RESULTS

Ten of 19 (52%) were NOTCH1 mutated: 5 in group A (45%) and 5 in group B (62.5%) with a favourable clinical outcome observed among this cohort with 28.7 (range 1-99) months of follow-up.

CONCLUSION

In conclusion, we identified a significant (52%) incidence of NOTCH1 mutations in CLL in the context of biclonal LPD, associated with an indolent clinical course.

Clinical considerations about the coexistence of melanoma and chronic lymphocytic leukemia in the era of targeted therapies, triggered by rare clinical scenarios. A case series and review of the literature

The epidemiologic correlation of melanoma and chronic lymphocytic leukemia (CLL) has been the subject of several population studies. In the present article, through the presentation of five illustrative cases of patients with melanoma and CLL, several aspects of this complex relationship are highlighted, with a focus on the increased incidence of melanoma in patients with CLL, its speculated etiology, and the impact of CLL stage and disease duration on the incidence and prognosis of melanoma. Furthermore, the rare entity of the synchronous diagnosis of melanoma and CLL in biopsied lymph nodes is discussed, along with its implications on the diagnostic and therapeutic procedures. In addition, the available data on the treatment choices in patients with melanoma and CLL are presented and the efficacy and safety of fludarabine, anti-CD20 monoclonal antibodies, new targeted therapies for CLL, and checkpoint inhibitors are further discussed. Finally, since no formal guidelines are available for the management of this group of patients, guidelines are proposed for skin-cancer screening in patients with CLL, for the correct interpretation of BRAF mutation analysis in lymph-node specimens with ‘collision of tumors,’ and for the optimal use of imaging studies in the diagnosis of metastatic disease in patients with CLL and melanoma, while a treatment approach for such patients is also suggested. The information and proposed guidelines provided in the present article comprise a useful guide for physicians managing such patients, focusing on diagnostic challenges and therapeutic dilemmas posed by the coexistence of the two disease entities.

BRAFV600E mutation in hairy cell leukemia: A single-center experience

Background

BRAFV600E mutation has been reported as a unique genetic lesion of hairy cell leukemia (HCL), a subset of which lacks this lesion and shows adverse outcomes.

Aims

To determine the prevalence of BRAFV600E in HCL from our center and derive clinicopathological correlation, if any.

Materials and Methods

A 9-year retrospective analysis of 46 consecutive cases of HCL diagnosed on morphology and immunophenotyping was done. Stained smears were used as samples for amplification refractory mutation system polymerase-chain reaction using fluorescent primers for mutation detection.

Results

BRAFV600E mutation was detected in 41/46 patients (89.1%) while absent in control samples of chronic lymphocytic leukemia. Cases mimicking HCL-variant clinically or immunophenotypically too showed the presence of this mutation. HCL with mutated BRAF presented at a younger age. No statistical difference in blood counts, tumor load, and immunophenotype patterns existed among BRAF mutated and unmutated group. Nine patients (45%) with mutated BRAF had residual disease following treatment with cladribine.

Conclusion

BRAFV600E mutation analysis has a definitive role in the diagnosis of HCL.

High-throughput sequencing of nodal marginal zone lymphomas identifies recurrent BRAF mutations

Nodal marginal zone lymphoma (NMZL) is a rare small B-cell lymphoma lacking disease-defining phenotype and precise diagnostic markers. To better understand the mutational landscape of NMZL, particularly in comparison to other nodal small B-cell lymphomas, we performed whole-exome sequencing, targeted high-throughput sequencing, and array-comparative genomic hybridization on a retrospective series. Our study identified for the first time recurrent, diagnostically useful, and potentially therapeutically relevant BRAF mutations in NMZL. Sets of somatic mutations that could help to discriminate NMZL from other closely related small B-cell lymphomas were uncovered and tested on unclassifiable small B-cell lymphoma cases, in which clinical, morphological, and phenotypical features were equivocal. Application of targeted gene panel sequencing gave at many occasions valuable clues for more specific classification.

BRAFV600E accelerates disease progression and enhances immune suppression in a mouse model of B-cell leukemia

Mutated mitogen-activated protein kinase (MAPK) pathway components promote tumor survival, proliferation, and immune evasion in solid tumors. MAPK mutations occur in hematologic cancers as well, but their role is less clear and few models are available to study this. We developed an in vivo model of disseminated BRAF^V600E B-cell leukemia to determine the effects of this mutation on tumor development and immune evasion. Mice with B-cell-restricted BRAF^V600E expression crossed with the Eµ-TCL1 model of chronic lymphocytic leukemia (CLL) developed leukemia significantly earlier (median, 4.9 vs 8.1 months; P < .001) and had significantly shorter lifespan (median, 7.3 vs 12.1 months; P < .001) versus BRAF wild-type counterparts. BRAF^V600E expression did not affect B-cell proliferation but reduced spontaneous apoptosis. BRAF^V600E-mutant leukemia produced greater T-cell effects, evidenced by exhaustion immunophenotype and CD44⁺ T-cell percentage, as well as increased expression of PD-L1 on CD11b⁺ cells. Results were confirmed in syngeneic mice engrafted with BRAF^V600E leukemia cells. Furthermore, a BRAF^V600E-expressing CLL cell line more strongly inhibited anti-CD3/CD28-induced T-cell proliferation, which was reversed by BRAF^V600E inhibition. These results demonstrate the immune-suppressive impact of BRAF^V600E in B-cell leukemias and introduce a new model to develop rational combination strategies targeting both tumor cells and tumor-mediated immune evasion.

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).

Somatic mutations in solid tumors: a spectrum at the service of diagnostic armamentarium or an indecipherable puzzle? The morphological eyes looking for BRAF and somatic molecular detections on cyto-histological samples

This review article deals with the analysis and the detection of the morphological features associated with somatic mutations, mostly BRAFV600E mutation, on both cytological and histological samples of carcinomas. Few authors demonstrated that some architectural and specific cellular findings (i.e. polygonal eosinophilic cells defined as "plump cells" and sickle-shaped nuclei) are able to predict BRAF V600E mutation in both cytological and histological samples of papillary thyroid carcinoma (PTC) as well as in other carcinomas. In the current review article we evaluated the first comprehensive analysis of the morphological prediction of BRAFV600E and other somatic mutations in different malignant lesions with the description of the possible mechanisms beneath these morphologic features. The detection of predictive morphological features, mostly on FNAC, may add helpful information to the stratification of the malignant risk and personalized management of cancers. Additionally, the knowledge of the molecular mechanism of different oncogenic drivers can lead to the organ-specific triaging selection of cases and can provide significant insight for targeted therapies in different malignant lesions.

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.

BRAFV600E induces ABCB1/P-glycoprotein expression and drug resistance in B-cells via AP-1 activation

A subset of patients with chronic lymphocytic leukemia (CLL) and nearly all patients with classic hairy cell leukemia (HCL) harbor somatic BRAF activating mutations. However, the pathological role of activated BRAF in B-cell leukemia development and progression remains unclear. In addition, although HCL patients respond well to the BRAFV600E inhibitor vemurafenib, relapses are being observed, suggesting the development of drug resistance in patients with this mutation. To investigate the biological role of BRAFV600E in B-cell leukemia, we generated a CLL-like B-cell line, OSUCLL, with doxycycline-inducible BRAFV600E expression. Microarray and real-time PCR analysis showed that ABCB1 mRNA is upregulated in these cells, and P-glycoprotein (P-gp) expression as well as function were confirmed by immunoblot and rhodamine exclusion assays. Additionally, pharmacological inhibition of BRAFV600E and MEK alleviated the BRAFV600E-induced ABCB1/P-gp expression. ABCB1 reporter assays and gel shift assays demonstrated that AP-1 activity is crucial in this mechanism. This study, uncovers a pathological role for BRAFV600E in B-cell leukemia, and provides further evidence that combination strategies with inhibitors of BRAFV600E and MEK can be used to delay disease progression and occurrence of resistance.

The utility of BRAF V600E mutation-specific antibody VE1 for the diagnosis of hairy cell leukemia

OBJECTIVES

BRAF V600E mutation is characteristic of hairy cell leukemia (HCL). A V600E mutation-specific antibody, VE1, has been recently developed. We studied the diagnostic utility of this antibody in HCL and compared it with other B-cell neoplasms.

METHODS

VE1 activity was assessed using immunohistochemistry in 90 mature B-cell neoplasms, including HCL (n = 17), HCL variant (n = 6), chronic lymphocytic leukemia (CLL) (n = 20), and 47 other B-cell lymphomas. Most (87/90) specimens were formalin-fixed, paraffin-embedded bone marrow (BM) biopsy specimens decalcified in either hydrochloric acid or formic acid.

RESULTS

VE1 was positive in 15 (88%) cases of HCL and two (10%) cases of CLL and was negative in all other tumors assessed. The VE1-positive HCL cases showed uniform staining in all tumor cells, but intensity was variable. The two VE1-negative HCL cases had BRAF V600 mutations proven by molecular analysis. The two CLL cases positive with VE1 showed an atypical staining pattern with expression in a minority of lymphoma cells. Immunohistochemistry using the VE1 antibody had a sensitivity of 88% and a specificity of 97% for HCL.

CONCLUSIONS

VE1 immunohistochemistry is a useful and convenient surrogate for detecting BRAF V600E mutation in BM biopsy specimens decalcified with hydrochloric or formic acid-based solutions.

Evaluation of allele-specific PCR and immunohistochemistry for the detection of BRAF V600E mutations in hairy cell leukemia

OBJECTIVES

Detection of BRAF V600E mutations in hairy cell leukemia (HCL) has important diagnostic utility. In this study, we sought to compare immunohistochemistry with an antibody specific for this mutation to a sensitive molecular assay.

METHODS

The performance of the BRAF V600E-specific VE1 antibody was compared with that of allele-specific polymerase chain reaction (PCR) in 22 formalin-fixed, paraffin-embedded (FFPE) specimens with HCL involvement, along with nine splenic marginal zone lymphomas (SMZLs), 10 follicular lymphomas (FLs), 10 mantle cell lymphomas (MCLs), and 10 chronic lymphocytic leukemia/small lymphocytic lymphomas (CLL/SLLs). An additional 11 SMZLs, 100 FLs, 20 MCLs, 83 CLL/SLL specimens, and 49 reactive tonsils within tissue microarrays were stained with VE1.

RESULTS

A BRAF V600E mutation was detected in 17 (77.3%) of 22 HCL cases by PCR. Immunohistochemistry demonstrated VE1 staining in 20 (90.9%) cases, identifying low-level (~1%) involvement in three HCL cases that were mutation negative by PCR. Evaluation of additional material from these patients confirmed the presence of BRAF V600E. Thirty-nine non-HCL cases were negative by both methods. Within tissue microarrays, weak false-positive staining was observed in two (0.8%) of 263 non-HCL cases.

CONCLUSIONS

VE1 immunohistochemistry is more sensitive than allele-specific PCR in FFPE bone marrow specimens and can be applied to decalcified core biopsy specimens that are not appropriate for molecular techniques.

BRAF--a new player in hematological neoplasms

BRAF oncogenic kinase has become a target for specific therapy in oncology. Genetic characterization of a predominant V600E mutation in melanoma, thyroid cancer, and other tumors became a focus for developing specific inhibitors, such as vemurafenib or dabrafenib. Our knowledge regarding the role of mutated BRAF in hematological malignancies has grown quickly as a result of new genetic techniques such as next-generation sequencing. This review summarizes current knowledge regarding the role of BRAF in lymphoid and myeloid neoplasms, with a focus on hairy-cell leukemia, Langerhans cell histiocytosis, and Erdheim-Chester disease.

An immunophenotypic and molecular diagnosis of composite hairy cell leukaemia and chronic lymphocytic leukaemia

Hairy cell leukaemia (HCL) and chronic lymphocytic leukaemia (CLL) are distinct clinicopathological B cell chronic lymphoproliferative disorders (B-CLPD). Both diseases have characteristic immunophenotypic and molecular features. The co-existence of two B-CLPD is perhaps more common than previously thought but a composite HCL and CLL has been rarely documented. A case is reported in which the morphology, integrated with an extensive immunophenotyping panel, and incorporation of the recently described HCL-associated BRAF V600E mutation, enabled the prompt diagnosis of composite HCL and CLL thus allowing appropriate treatment selection. This case serves to highlight the benefit of a multidisciplinary approach to the diagnosis of bi-clonal B-CLPD.

Phospho-ERK(THR202/Tyr214) is overexpressed in hairy cell leukemia and is a useful diagnostic marker in bone marrow trephine sections

BRAF V600E mutations are present in virtually all cases of hairy cell leukemia (HCL). We hypothesized that detection of phospho-ERK (pERK) in tissue sections may be a useful marker for diagnosis of HCL. pERK/CD20 double immunostaining was performed on 90 formalin-fixed bone marrow trephine samples affected with small B-cell lymphoproliferative disorders, including 28 cases of HCL. pERK staining was observed in all 28 cases of HCL and in 1 of 62 cases of non-HCL B-cell lymphoproliferative disorders. By allele-specific polymerase chain reaction, all 11 cases of HCL with available DNA were positive for BRAF V600E, as was the 1 pERK non-HCL case. The remaining 31 non-HCL cases tested were negative for BRAF V600E. The sensitivity and specificity of pERK for diagnosis of HCL was 100% and 98%, respectively. We conclude that the presence of pERK as detected by immunohistochemical staining is a useful surrogate marker for BRAF V600E in the diagnosis of HCL.

Investigation of the BRAF V600E mutation by pyrosequencing in lymphoproliferative disorders

The presence of the BRAF c.1799T>A V600E mutation was recently described in cases of hairy cell leukemia (HCL) but not in other common lymphomas. However, many uncommon subtypes of lymphoma have not been studied. We designed a BRAF pyrosequencing assay specific for the V600E mutation, which has a sensitivity of 5% and is applicable to paraffin-embedded tissue. DNA was sequenced in 9 cases of HCL; 6 cases of variant HCL; 10 cases each of nodal marginal zone lymphoma (NMZL), extranodal marginal zone lymphoma (ENMZL), posttransplantation lymphoproliferative disorder (PTLD), and large granular lymphocyte (LGL) proliferations; 11 cases of peripheral T-cell lymphoma (PTCL); and 12 cases of anaplastic large cell lymphoma (ALCL). All (100%) cases of HCL were positive for BRAF mutations. No mutations were identified in variant HCL, NMZL, ENMZL, PTLD, PTCL, ALCL, or LGL proliferations. Among lymphoproliferative disorders, BRAF mutations are restricted to HCL.

BRAF mutations in chronic lymphocytic leukemia

BRAF mutations have been shown to occur at a high frequency in melanoma and thyroid cancer, but also at lower frequencies in hematological malignancies. To assess the potential role of BRAF, we have sequenced exons 11 and 15 of BRAF in 138 cases with chronic lymphocytic leukemia (CLL) and 32 cases of B-cell prolymphocytic leukemia (B-PLL). We found an incidence of BRAF mutations of 2.8% in CLL (4/138), while no cases with B-PLL showed BRAF mutations. The analysis of a cohort of patients with fludarabine-refractory disease (n = 87) showed no increase in the mutation incidence, suggesting that this mutation is not selected for during the disease progression. A limited analysis of the effect of BRAF inhibition in primary CLL cells showed no cell death induction in CLL samples with and without BRAF mutations. Our analysis suggests that BRAF mutations occur at a low frequency in CLL. The pharmacological inhibition of MEK/ERK signaling using the mutant BRAF inhibitor PLX4720 showed no effect on viability in vitro in CLL cases.