Detection of activating MAP2K1 mutations in atypical hairy cell leukemia and hairy cell leukemia variant

Detangling the Threads of Hairy Cell Leukemia, Beyond the Morphology and Into the Molecular

Hairy cell leukemia (HCL) makes up 2% of leukemias in the United States and encompasses great molecular heterogeneity. The standard treatment paradigm involves purine nucleoside analogues in the upfront setting with high complete response rate to initial therapy but frequent relapses. There is an increasing role for BRAF inhibitors, with or without rituximab, in refractory and even in untreated patients. The response to purine analogues in HCL variant cases, otherwise classified as splenic lymphoma with prominent nucleolus in the 5th WHO edition classification, is less robust. Several antibodies, small molecular inhibitors, and combination regimens have been explored in HCL but data is frequently limited by case reports or small case series. Here we review available treatment options including their efficacy and safety profiles. We also explore investigational agents and potential future targets. The goal is to present a comprehensive therapeutic review of this rare disease entity and outline the ever increasing and novel therapeutic management options which interrupt key pathways in the pathogenesis of this malignancy.

The fifth edition of the WHO classification of mature B-cell neoplasms: open questions for research

The fifth edition of the World Health Organization Classification of Haematolymphoid Tumours (WHO-HAEM5) is the product of an evidence-based evolution of the revised fourth edition with wide multidisciplinary consultation. Nonetheless, while every classification incorporates scientific advances and aims to improve upon the prior version, medical knowledge remains incomplete and individual neoplasms may not be easily subclassified in a given scheme. Thus, optimal classification requires ongoing study, and there are certain aspects of some entities and subtypes that require further refinements. In this review, we highlight a selection of these challenging areas to prompt more research investigations. These include (1) a 'placeholder term' of splenic B-cell lymphoma/leukaemia with prominent nucleoli (SBLPN) to accommodate many of the splenic lymphomas previously classified as hairy cell leukaemia variant and B-prolymphocytic leukaemia, a clear new start to define their pathobiology; (2) how best to classify BCL2 rearrangement negative follicular lymphoma including those with BCL6 rearrangement, integrating the emerging new knowledge on various germinal centre B-cell subsets; (3) what is the spectrum of non-IG gene partners of MYC translocation in diffuse large B-cell lymphoma/high-grade B-cell lymphoma and how they impact MYC expression and clinical outcome; how best to investigate this in a routine clinical setting; and (4) how best to define high-grade B-cell lymphoma not otherwise specified and high-grade B-cell lymphoma with 11q aberrations to distinguish them from their mimics and characterise their molecular pathogenetic mechanism. Addressing these questions would provide more robust evidence to better define these entities/subtypes, improve their diagnosis and/or prognostic stratification, leading to better patient care. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Molecular Targeting of the BRAF Proto-Oncogene/Mitogen-Activated Protein Kinase (MAPK) Pathway across Cancers

The mitogen-activated protein kinase (MAPK) pathway is essential for cellular proliferation, growth, and survival. Constitutive activation of this pathway by BRAF mutations can cause downstream activation of kinases, leading to uncontrolled cellular growth and carcinogenesis. Therefore, inhibition of BRAF and the downstream substrate MEK has been shown to be effective in controlling tumor growth and proliferation. Over the last decade, several BRAF and MEK inhibitors have been investigated, ranging from primarily melanoma to various cancer types with BRAF alterations. This subsequently led to several Food and Drug Administration (FDA) approvals for BRAF/MEK inhibitors for melanoma, non-small cell lung cancer, anaplastic thyroid cancer, colorectal cancer, histiocytosis neoplasms, and finally, tumor-agnostic indications. Here, this comprehensive review will cover the developments of BRAF and MEK inhibitors from melanomas to tumor-agnostic indications, novel drugs, challenges, future directions, and the importance of those drugs in personalized medicine.

Splenic B-cell lymphoma/leukemia with prominent nucleoli: A three-case series of the newly named old entity and review of literature

CONTEXT

Splenic B-cell lymphoma/leukemia with prominent nucleoli (SBLPN) aka hairy cell leukemia variant (HCL-v) is a rare B-cell chronic lymphoproliferative disorder. The main diagnostic challenge is to differentiate SBLPN from Classical hairy cell leukemia (HCL-c), as the former faces inferior responses to therapies and a poor prognosis.

AIMS

The aim is to discuss the clinic-hematological and immunophenotyping findings of three cases of SBLPN.

SETTINGS AND DESIGN

This is a retrospective observational study.

METHODS AND MATERIAL

From the year 2011 to 2021, flow cytometry of all the cases with HCL diagnosis was reviewed, and three cases with negative or dim CD25 and hematological presentation matching with SBLPN were picked up.

STATISTICAL ANALYSIS USED

Descriptive statistics is used.

RESULTS

All the cases were male. The age ranges from 43 to 64 years. Median hemoglobin concentration, total leucocyte count, and platelet count were 8.6 g/dL, 6.9 × 109/L, and 53 × 109/L, respectively. The atypical cells were medium to large. All three showed prominent nucleoli. Bone marrow biopsies showed an interstitial pattern of infiltration in all the cases. The hairy cells were positive for CD20, CD11c, and CD103. CD25 was dim positive in one case. Annexin A1 was negative in all three cases. BRAF V600E mutation analysis was done in one case and turned out negative for the mutation.

CONCLUSIONS

SBLPN is a rare entity, usually on-flow cytometry CD25 negative. However, in dim CD25-positive cases, BRAFV600E mutational analysis helps in discerning SBLPN diagnosis and differentiating it from HCL-c.

Clinical, Morphologic, and Molecular Features of Benign and Intermediate-grade Melanocytic Tumors With Activating Mutations in MAP2K1

Activating mutations in MAP2K1 can be seen in benign and intermediate-grade melanocytic neoplasms with spitzoid morphology. We analyzed the clinical, histopathologic, and genetic features for 16 cases of benign and intermediate-grade melanocytic tumors harboring activating MAP2K1 mutations. We compared them to Spitz neoplasms with characteristic Spitz fusions or HRAS mutation. We also compared the mutational pattern of benign and intermediate-grade MAP2K1 -mutated neoplasms and melanomas with activating MAP2K1 mutations. Among the 16 cases, the favored morphologic diagnosis was Spitz nevus (8/16), atypical Spitz tumors (6/16), and deep penetrating nevus (2/16). The 2 most common architectural patterns seen included a plaque-like silhouette with fibroplasia around the rete reminiscent of a dysplastic nevus (n=7) or a wedge-shaped or nodular pattern with the plexiform arrangement of the nests aggregating around the adnexa or neurovascular bundle (n=8). The cases with dysplastic architecture and spitzoid cytology resembled dysplastic Spitz nevi. Compared with true Spitz neoplasms, MAP2K1 -mutated neoplasms occurred in older age groups and had more frequent pagetosis and a lower average mitotic count. The most common type of mutation in the benign and intermediate-grade cases in the literature involves an in-frame deletion, while, in melanomas, missense mutations are predominant. Benign and intermediate-grade melanocytic neoplasms with activating mutations in MAP2K1 can have morphologic overlap with Spitz neoplasms. A significant proportion of melanomas also have activating MAP2K1 mutations. In-frame deletions are predominantly seen in the benign and intermediate-grade cases, and missense mutations are predominantly seen in melanomas.

The many faces of nodal and splenic marginal zone lymphomas. A report of the 2022 EA4HP/SH lymphoma workshop

Session 3 of the lymphoma workshop of the XXI joint meeting of the European Association for Haematopathology and the Society for Hematopathology took place in Florence, Italy, on September 22, 2022. The topics of this session were splenic and nodal marginal zone lymphomas, transformation in marginal zone lymphomas, and pediatric nodal marginal zone lymphomas and their differential diagnosis as well as related entities. Forty-two cases in these categories were submitted to the workshop, including splenic lymphomas (marginal zone and diffuse red pulp lymphomas), transformed marginal zone lymphomas (splenic and nodal), nodal marginal zone lymphomas with increased TFH-cells, and pediatric nodal marginal zone lymphomas. The case review highlighted some of the principal problems in the diagnosis of marginal zone lymphomas, including the difficulties in the distinction between splenic marginal zone lymphoma, splenic diffuse red pulp lymphoma, and hairy cell leukemia variant/splenic B-cell lymphoma with prominent nucleoli which requires integration of clinical features, immunophenotype, and morphology in blood, bone marrow, and spleen; cases of marginal zone lymphoma with markedly increased TFH-cells, simulating a T-cell lymphoma, where molecular studies (clonality and mutation detection) can help to establish the final diagnosis; the criteria for transformation of marginal zone lymphomas, which are still unclear and might require the integration of morphological and molecular data; the concept of an overlapping spectrum between pediatric nodal marginal zone lymphoma and pediatric-type follicular lymphoma; and the distinction between pediatric nodal marginal zone lymphoma and "atypical" marginal zone hyperplasia, where molecular studies are mandatory to correctly classify cases.

Refractory and relapsed hairy-cell leukemia (HCL): casting light on promising experimental drugs in clinical trials

INTRODUCTION

Hairy cell leukemia (HCL) is a rare subtype of indolent lymphoid leukemia originating from a mature B lymphocyte. The standard first-line treatment for classic HCL, and HCL variant (HCLv), consists of purine nucleoside analogs (PNA), with or without rituximab. However, almost half of patients relapse and require subsequent therapy.

AREAS COVERED

This article summarizes recent achievements in the treatment of relapsed and refractory HCL. A literature search was conducted of the PubMed and MEDLINE database for articles in English. Publications from 2010 through January 2023 were scrutinized. The search terms used were hairy cell leukemia in conjunction with BRAF inhibitors, Bruton's tyrosine kinase (BTK) inhibitors, CD20 monoclonal antibodies, relapsed, refractory and variant.The growing understanding of HCL biology has allowed the design of several new, chemotherapy-free targeted drugs which have demonstrated encouraging efficacy in early clinical trials.

EXPERT OPINION

Novel drugs will soon be available to assist standard therapy for HCL and HCLv among patients with suboptimal results following PNA treatment. In particular, the BRAF inhibitors vemurafenib and dabrafenib, with or without rituximab, have revolutionized treatment of patients with relapsed or refractory disease.

Purine nucleoside analogs plus rituximab are an effective treatment choice for hairy cell leukemia-variant

Both characteristics and optimal treatment strategy for hairy cell leukemia-variant (HCL-v) remain elusive due to its rarity. We retrospectively analyzed the clinical features of HCL-v and the efficacy of first-line treatment options in a large Chinese cohort. In this study, we recruited 33 HCL-v patients (23 males and 10 females) with a median age of 59 years (range, 34-79 years). The chief complaints included abdominal mass and relative signs (67%) and abnormal complete blood count (27%). Immunophenotyping showed monoclonal B-cells positive for pan B-cell antigens and CD11c, weakly positive for CD103 and CD200, while negative for CD5, CD10, CD25, CD123, and annexin A1. No BRAF V600E mutation was detected, but TP53 abnormality was recurrent. Treatment choices included interferon-α (IFN-α) in 11 patients, chlorambucil (CLB) in 5 patients, single purine nucleoside analogs (PNA) in 3 patients, PNA plus rituximab (PNA + R) in 9 patients, and others in 3 patients. Four patients who received IFN-α or CLB treatment also underwent splenectomy. Patients who received PNA + R had a higher complete response rate (88% versus 5%, P < 0.001) and longer progression-free survival (PFS, 3-year PFS rate 42% [95% CI 1-84] vs. 16% [95% CI 3-40], P = 0.042) than those who received other regimens. Overall, HCL-v is an indolent lymphoma with unique characteristics. The PNA + R regimen is the preferred choice in the first-line treatment for HCL-v.

Updates in hairy cell leukemia (HCL) and variant-type HCL (HCL-V): rationale for targeted treatments with a focus on ibrutinib

Hairy cell leukemia (HCL) and HCL-like disorders such as hairy cell leukemia variant (HCL-V) and splenic diffuse red pulp lymphoma (SDRPL) are rare indolent B-cell malignancies. Purine analogs (PNAs), alone or in association with rituximab (R), are the standard of care for HCL in the first-line setting. However, PNAs are toxic and patients may become resistant to these drugs. Therefore, new therapeutic strategies are needed. Several recent in vitro studies highlighted the importance of the interactions between HCL cells and their microenvironment, in particular with bone marrow stromal cells, endothelial cells, and the extracellular matrix. In these interactions, chemokine receptors and adhesion molecules play a major role. Moreover, the importance of signaling pathways, like BRAF, BCR, and CXCR4 has been underlined. Bruton's tyrosine kinase (BTK) is a fundamental signal transmitter of BCR and CXCR4 in HCL. Preclinical and recent clinical data showed an efficacy of ibrutinib, a BTK inhibitor (BTKi), in HCL and HCL-V. These promising results joined those of other emerging drugs like BRAF or MEK inhibitors and anti-CD22 immunotoxins.

Plain Language Summary

Bruton's tyrosine kinase (BTK) inhibitors (BTKi) in hairy cell leukemia (HCL) and variant-type HCL The treatment of hairy cell leukemia (HCL) has changed significantly in recent years. In the first-line settings, treatment with purine analogs (PNAs) with or without anti-CD20 monoclonal antibodies remains the gold standard in 2022. In relapsed/refractory HCL, other drugs are needed: BRAF inhibitors: vemurafenib monotherapy with or without rituximab or dabrafenib in combination with trametinib, an MEK inhibitor (MEKi), as well as the anti-CD22 antibody drug conjugate moxetumomab pasudotox.There are arguments for the use of Bruton's tyrosine kinase inhibitors (BTKi). Ibrutinib was recently tested in a multisite phase 2 study in 37 patients with either HCL (28 patients: 76%) or HCL-V (nine patients: 24%) including two who were previously untreated. Patients received single-agent ibrutinib at 420 mg daily (24 patients) or 840 mg daily (13 patients) until disease progression or unacceptable toxicity. The overall response rate (ORR) at 32 weeks was 24%, increasing to 36% at 48 weeks and reaching 54% at any time since starting ibrutinib. Seven patients achieved a complete response (CR) as the best response at any time on study, while 13 patients had a partial response (PR) and 10 patients had stable disease (SD). Interestingly, the response rate was not statistically different between HCL and HCL-V patients, suggesting that ibrutinib could be an option in both entities. The estimated 36-month progression-free survival (PFS) was 73% and the estimated 36-month overall survival (OS) was 85%, with no differences between HCL and HCL-V. The frequency of cardiovascular grade 1-2 adverse events (AEs) was 16% for atrial fibrillation; 3% for atrial flutter; 32% for hypertension; and 0%, 3%, and 11%, respectively, for grade ⩾ 3 AEs. Unlike in chronic lymphocytic leukemia (CLL), where the mechanism of action of ibrutinib is well known, the mechanism of action of ibrutinib in HCL appears to be unclear. No mutations were identified in patients with progressive disease, suggesting that the mechanisms of resistance could be different between HCL and CLL. The BTKi that are not yet approved are challenged by the new other targeted treatments.

Deciphering Genetic Alterations of Hairy Cell Leukemia and Hairy Cell Leukemia-like Disorders in 98 Patients

Simple Summary

The diagnosis of hairy cell leukemia (cHCL) and HCL-like disorders, including the variant form of HCL (vHCL) and splenic diffuse red pulp lymphoma (SDRPL) can be challenging, particularly in complex situations. The integration of all data, including molecular data, is essential for distinguishing the different entities. The BRAF^V600E mutation is identified in most cHCL cases, whereas it is absent in vHCL and SDRPL. MAP2K1 mutations are observed in half of vHCL cases and in cHCL BRAF^WT and they are associated with a worse prognosis. The interest in deep sequencing for the diagnosis and prognosis of hairy cell leukemia and HCL-like disorders is essential. Some KLF2 genetic alterations have been localized on the AID consensus motif, suggesting an AID-induced mutation mechanism. KLF2 is the second most altered gene in HCL, and mutations must be investigated to confirm whether AID could be responsible for the genetic alterations in this gene. Clonal evolution can be observed in half of the cases.

Abstract

Hairy cell leukemia (cHCL) patients have, in most cases, a specific clinical and biological presentation with splenomegaly, anemia, leukopenia, neutropenia, monocytopenia and/or thrombocytopenia, identification of hairy cells that express CD103, CD123, CD25, CD11c and identification of the V600E mutation in the B-Raf proto-oncogene (BRAF) in 90% of cases. Monocytopenia is absent in vHCL and SDRPL patients and the abnormal cells do not express CD25 or CD123 and do not present the BRAF^V600E mutation. Ten percent of cHCL patients are BRAF^WT and the distinction between cHCL and HCL-like disorders including the variant form of HCL (vHCL) and splenic diffuse red pulp lymphoma (SDRPL) can be challenging. We performed deep sequencing in a large cohort of 84 cHCL and 16 HCL-like disorders to improve insights into the pathogenesis of the diseases. BRAF mutations were detected in 76/82 patients of cHCL (93%) and additional mutations were identified in Krüppel-like Factor 2 (KLF2) in 19 patients (23%) or CDKN1B in 6 patients (7.5%). Some KLF2 genetic alterations were localized on the cytidine deaminase (AID) consensus motif, suggesting AID-induced mutations. When analyzing sequential samples, a clonal evolution was identified in half of the cHCL patients (6/12 pts). Among the 16 patients with HCL-like disorders, we observed an enrichment of MAP2K1 mutations in vHCL/SDRPL (3/5 pts) and genes involved in the epigenetic regulation (KDM6A, EZH2, CREBBP, ARID1A) (3/5 pts). Furthermore, MAP2K1 mutations were associated with a bad prognosis and a shorter time to next treatment (TTNT) and progression-free survival (PFS), independently of the HCL classification.

Advances in the Treatment of Hairy Cell Leukemia Variant

OPINION STATEMENT

Hairy cell leukemia variant (HCL-V) is a rare B cell lymphoproliferative disorder with a clinical-pathological distinction from the classic form of hairy cell leukemia (HCL-C). HCL-V is more aggressive in nature, has a higher tendency to be refractory to conventional purine analog pharmacotherapies, and leads to a poorer prognosis. Hence, these differing features bring paramount importance to the diagnosis and management of HCL-V. While there is no genetic mutation diagnostic of HCL-V, genetic profiling efforts have identified potential therapeutic targets (i.e., MAP2K1, KDM6A, CREBBP, ARID1A, CCND3, U2AF1, KMT2C) and yielded prognostic markers (i.e., IGHV4-34 rearrangements). To date, combination chemoimmunotherapies, such as cladribine and rituximab, have shown the best results in HCL-V. Future directions include targeted therapies such as moxetumomab pasudotox, ibrutinib, trametinib, and binimetinib and potentially anti-CD22 chimeric antigen receptor T cell therapy. The purpose of this review is to provide an outline of the diagnostic approach and an update on the therapeutic advancements in HCL-V.

The Genomics of Hairy Cell Leukaemia and Splenic Diffuse Red Pulp Lymphoma

Classical hairy cell leukaemia (HCLc), its variant form (HCLv), and splenic diffuse red pulp lymphoma (SDRPL) constitute a subset of relatively indolent B cell tumours, with low incidence rates of high-grade transformations, which primarily involve the spleen and bone marrow and are usually associated with circulating tumour cells characterised by villous or irregular cytoplasmic borders. The primary aim of this review is to summarise their cytogenetic, genomic, immunogenetic, and epigenetic features, with a particular focus on the clonal BRAFV600E mutation, present in most cases currently diagnosed with HCLc. We then reflect on their cell of origin and pathogenesis as well as present the clinical implications of improved biological understanding, extending from diagnosis to prognosis assessment and therapy response.

Clinical Utility of Targeted Next-Generation Sequencing in the Evaluation of Low-Grade Lymphoproliferative Disorders

OBJECTIVES

We investigated the usefulness of a custom-designed 31-gene next-generation sequencing (NGS) panel implemented on a routine basis for the evaluation of low-grade lymphoproliferative disorders (LPDs).

METHODS

In total, 147 blood, bone marrow, and tissue specimens were sequenced, including 81% B-cell, 15% T-cell, and 3% natural killer (NK)-cell neoplasms.

RESULTS

Of the cases, 92 (63%) of 147 displayed at least one pathogenic variant while 41 (28%) of 147 had two or more. Low mutation rates were noted in monoclonal B-cell lymphocytoses and samples with small T- and NK-cell clones of uncertain significance. Pathogenic molecular variants were described in specific disorders and classified according to their diagnostic, prognostic, and potential therapeutic value. Diagnostically, in addition to confirming the diagnosis of 15 of 15 lymphoplasmacytic lymphomas, 10 of 12 T large granular lymphocytic leukemias, and 2 of 2 hairy cell leukemias (HCLs), the panel helped resolve the diagnosis of 10 (62.5%) of 16 challenging cases lacking a specified diagnosis based on standard morphology, phenotype, and genetic analysis.

CONCLUSIONS

Overall, implementation of this targeted lymphoid NGS panel as part of regular hematopathology practice was found to be a beneficial adjunct in the evaluation of low-grade LPDs.

Diagnostic and therapeutic challenges in hairy cell leukemia-variant: where are we in 2021?

INTRODUCTION

Hairy cell leukemia-variant (HCL-V) is a rare B-cell neoplasm arising or homing primarily in the spleen. It has been considered in the WHO classification of Hemopoietic and Lymphoid Tumors as a provisional entity since 2008 and included under the umbrella of unclassifiable splenomegalic B-cell leukemia/lymphomas. The diagnosis is a challenge to hematopathologists and management of these patients by the clinicians is difficult due to the lack of diagnostic and therapeutic guidelines and prospective studies.

AREAS COVERED

This manuscript is a comprehensive review of the clinical features, pathology, immunophenotypic profile, genomic alterations and therapeutic options of HCL-V. Diagnostic and therapeutic dilemmas are extensively outlined considering the information derived from a literature search covering from 1980 to 2019. Integration of all the data is needed and recommended for establishing the diagnosis of this leukemia.

EXPERT OPINION

More extensive information of genomic aberrations underlying the pathogenesis of the disease would be a solid stone for the diagnosis. To this end, a collaborative work among scientists and pathologists from different centers is required and expected. In turn, this might have a relevant clinical translation by allowing to identify putative targets for therapy and to improve the outlook of these patients.

Current and Emerging Therapeutic Options for Hairy Cell Leukemia Variant

Hairy cell leukemia variant (HCL-v) is a rare B-cell lymphoproliferative disorder with distinct immunophenotypic and molecular characteristics when compared to classical hairy cell leukemia (HCL-c). In contrast to the enormous progress in therapeutic options for HCL-c, HCL-v remains a therapeutic challenge due to inferior outcomes with standard chemoimmunotherapy and BCR signaling pathway inhibitors, and due to the fact that HCL-v has limited molecular therapeutic targets. In addition, because of the rarity of the disease, there is a paucity of later phase studies or multicenter trials to guide treatment decisions. In this article, we briefly review the diagnostic criteria and clinical characteristics of HCL-v and present a comprehensive overview of current therapeutic options in HCL-v.

Melanoma with in-frame deletion of MAP2K1: a distinct molecular subtype of cutaneous melanoma mutually exclusive from BRAF, NRAS, and NF1 mutations

While the genomics of BRAF, NRAS, and other key genes influencing MAP kinase (MAPK) activity have been thoroughly characterized in melanoma, mutations in MAP2K1 (MEK1) have received significantly less attention and have consisted almost entirely of missense mutations considered secondary oncogenic drivers of melanoma. Here, we investigated melanomas with in-frame deletions of MAP2K1, alterations characterized as MAPK-activating in recent experimental models. Our case archive of clinical melanoma samples with comprehensive genomic profiling by a hybrid capture-based DNA sequencing platform was searched for MAP2K1 genetic alterations. Clinical data, pathology reports, and histopathology were reviewed for each case. From a cohort of 7119 advanced melanomas, 37 unique cases (0.5%) featured small in-frame deletions in MAP2K1. These included E102_I103del (n = 11 cases), P105_A106del (n = 8), Q58_E62del (n = 6), I103_K104del (n = 5), I99_K104del (n = 3), L98_I103del (n = 3), and E41_F53del (n = 1). All 37 were wild type for BRAF, NRAS, and NF1 genomic alterations ("triple wild-type"), representing 2.0% of triple wild-type melanomas overall (37/1882). Median age was 66 years and 49% were male. The majority arose from primary cutaneous sites (35/37; 95%) and demonstrated a UV signature when available (21/25; 84%). Tumor mutational burden was typical for cutaneous melanoma (median = 9.6 mut/Mb, range 0-35.7), and frequently mutated genes included TERTp (63%), CDKN2A (46%), TP53 (11%), PTEN (8%), APC (8%), and CTNNB1 (5%). Histopathology revealed a spectrum of appearances typical of melanoma. For comparison, we evaluated 221 cases with pathogenic missense single nucleotide variants in MAP2K1. The vast majority of melanomas with missense SNVs in MAP2K1 showed co-mutations in BRAF (58%), NF1 (23%), or NRAS (18%). In-frame deletions in MAP2K1, previously shown in experimental models to be strongly MAPK-activating, characterized a significant subset of triple wild-type melanoma (2.0%), suggesting a primary oncogenic role for these mutations. Comprehensive genomic profiling of melanomas enables detection of this alteration, which may have implications for potential therapeutic options.

Melanocytic Neoplasms With MAP2K1 in Frame Deletions and Spitz Morphology

With the advent of better molecular characterization of Spitz melanocytic neoplasms, there has been increasing effort to better understand and describe the relationships between specific driver fusion and/or mutations with the clinical and histomorphological characteristics of the lesions. Structural rearrangements in mitogen activated protein kinase genes have recently been noted to be important in Spitz neoplasms. Only very few reports, however, have described in detail melanocytic tumors with in frame deletions in MAP2K1. Cases in the literature with this aberration have been described as having a diagnosis of Spitz, deep penetrating nevi, or pigmented epithelioid melanocytoma. In this study, we describe a cohort of 6 cases with MAP2K1 activating in frame deletions. The morphologic spectrum of the cases was broad. Common features of these cases include Spitzoid cytomorphology (5/6) cases, prominent melanin pigmentation (4/6) cases, and deep penetrating nevi-like plexiform architecture (3/6) cases. The diagnoses at the time of clinical care of these cases included nevus of Reed (1/6), desmoplastic Spitz tumor (1/6), BAPoma (1/6), deep penetrating melanocytic nevus (2/6), and melanoma (1/6). Clinical follow-up was available in 3 of the 6 cases. None of the patients had a tumor recurrence. This builds on the growing literature to help expand the spectrum of changes associated with Spitzoid melanocytic neoplasms.

B-cell neoplasms and Hodgkin lymphoma in the spleen

B-cell lymphoma of spleen may be primary (most commonly splenic diffuse large B-cell lymphoma) or secondary (typically low-grade non-Hodgkin lymphoma). Depending on the specific lymphoma subtype, there may be a predominantly white pulp pattern of involvement, a predominantly red pulp pattern or a focal nodular pattern. Splenectomy is the ideal specimen for a multiparametric integrative diagnosis of splenic lymphoma, as it allows for a combined study of morphology, immunohistology, flow cytometry, cytogenetics, and molecular genetic techniques. This review article describes the clinicopathologic characteristics of all the relevant B-cell neoplasms that may be encountered in a splenic biopsy or a splenectomy specimen.

Biology and Treatment of Hairy Cell Leukemia

OPINION STATEMENT

Despite its rarity, hairy cell leukemia (HCL) remains a fascinating disease and the physiopathology is becoming more and more understood. The accurate diagnosis of HCL relies on the recognition of hairy cells by morphology and flow cytometry (FCM) in the blood and/or bone marrow (BM). The BRAF V600E mutation, an HCL-defining mutation, represents a novel diagnostic parameter and a potential therapeutic target. The precise cellular origin of HCL is a late-activated postgerminal center memory B cell. BRAF mutations were detected in hematopoietic stem cells (HSCs) of patients with HCL, suggesting that this is an early HCL-defining event. Watch-and-wait strategy is necessary in approximately 10% of asymptomatic HCL patients, sometimes for several years. Purine analogs (PNAs) are the established first-line options for symptomatic HCL patients. In second-line treatment, chemoimmunotherapy combining PNA plus rituximab should be considered in high-risk HCL patients. The three options for relapsed/refractory HCL patients include recombinant immunoconjugates targeting CD22, BRAF inhibitors, and BCR inhibitors. The clinical interest to investigate blood minimal residual disease (MRD) was recently demonstrated, with a high risk of relapse in patients with positive testing for MRD and a low risk in patients with negative testing. However, efforts must be made to standardize MRD analyses in the near future. Patients with HCL are at risk of second malignancies. The increased risk could be related to the disease and/or the treatment, and the respective role of PNAs in the development of secondary malignancies remains a topic of debate.

Expression of the muscle-associated gene MYF6 in hairy cell leukemia

Hairy cell leukemia (HCL) is a purine analog-responsive B-cell malignancy containing the BRAF V600E mutation, expressing CD22, CD11c, CD103, tartrate resistant acid phosphatase (TRAP) CD25, CD123, and annexin 1A. BRAF V600E and the latter 4 markers are usually absent in the more aggressive and chemoresistant variant HCLv. To evaluate differences between HCL and HCLv, expression microarrays comparing HCL with HCLv were performed for 24694 genes using 47323 probes. Microarray data from 35 HCL and 27 HCLv purified samples showed the greatest HCL-HCLv difference in the muscle-associated gene MYF6, expressed by its 2 probes 18.5- and 10.8-fold higher in HCL than HCLv (p<0.0001). By real-time quantitative PCR (RQ-PCR), 100% of 152 classic HCL samples were MYF6-positive, vs 5 (6%) of 90 blood donors. MYF6-expression was also detected in 18 (35%) of 51 with HCLv, 11 (92%) of 12 with HCL expressing unmutated IGHV4-34, 35 (73%) of 48 with chronic lymphocytic leukemia (CLL), and 1 (8%) of 12 with mantle cell lymphoma. Hypomethylation status of MYF6 supported expression in HCL more than HCLv. Posttreatment blood samples becoming negative by flow cytometry remained MYF6+ by RQ-PCR in 42 (48%) of 87 HCL patients, and MYF6 RQ-PCR could detect 1 HCL in 10⁵ normal cells. MYF6, universally expressed in HCL and in most CLL samples, may be a useful biomarker for these leukemias. Further studies are underway to determine the role of MYF6 in HCL.

Difference of genomic copy numbers alterations between hairy cell leukemia-variant and classical hairy cell leukemia: a pilot retrospective study in Chinese

Background: Hairy cell leukemia (HCL) is a rare chronic B-cell lymphoproliferative disorder. It has two pathological subtypes: classical HCL (HCL-C) and HCL-variant (HCL-V). HCL-C and HCL-V are distinct in morphology and immunophenotype. Their differentiation is important for patient management and clinical outcome, with HCL-V responding poorly to conventional HCL treatments. Recently, whole genomic sequencing has been used to identify the difference between HCL-C and HCL-V and mutation of BRAF^V600E has been proved to be a molecular hallmark of HCL-C. However, BRAF inhibitors were not effective in all HCL-C cases and HCL-V seems be lack of the high-frequency mutations. Therefore, it is necessary to compare the genomic changes between HCL-C and HCL-V by high-resolution studies, especially in Chinese population, the genomic alterations of HCL have rarely be reported. Methods: In this study, the clinical features of a total of 18 Chinese HCL patients were described. Single nucleotide polymorphism (SNP) array analysis was performed to evaluate the genomic copy number alterations (CNA) and copy neutral loss of heterozygosity (CN-LOH) on six HCL-Vs with CD25^-/BRAF^V600E- and four HCL-Cs with CD25⁺/BRAF^V600E+. Results: A total of 24 CNAs including seven chromosomal gains and 17 chromosomal losses, and 22 CN-LOHs were revealed. Five of the six cases of HCL-V showed 15 CNAs including four cryptic chromosomal gains and 11 chromosomal losses. Overlapping regions involving micro-deletion of chromosome 2q13 and large chromosomal loss of 14q were showed in HCL-V. In HCL-C, a total of nine CNAs were revealed in three of the four cases including three chromosomal gains and six chromosomal losses. No overlapping area was observed among the CNVs. 15 CN-LOHs were showed in five of the six cases of HCL-V and seven CN-LOHs was demonstrated in all of the four HCL-Cs. Conclusions: Comparing to Westerners, a relatively higher proportion of HCL-V in all HCL is observed in this study. CNAs and CN-LOHs were common in both HCL-V and HCL-C but the CNAs were different in them. HCL-C was characterized with the higher ratio of large chromosomal changes but lacked of recurrent CNAs, while HCL-V was presented with the higher incidence of cryptic CNAs and recurrent CNAs involving tumor-associated genes. It is necessary to further investigate the association of the genes, such as NPHP1 and TRAF3 genes, and HCL-V in the future study.

Hairy cell leukemia: present and future directions

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, with long-term responses to purine analogs, but with decreasing efficacy and increasing toxicity with repeated courses. Leukemic cells express CD22, CD20, CD25, tartrate-resistant acid phosphatase (TRAP), annexin 1A (Anxa1), and BRAF V600E mutation. HCLv, lacking CD25, Anxa1, TRAP, and BRAF V600E, is more aggressive and less purine analog-sensitive. A molecularly defined IGHV4-34+ variant is also resistant whether HCL or HCLv immunophenotypically. Traces of HCL cells, termed minimal residual disease (MRD), accompany most with complete remission (CR) and may cause relapse. Rituximab has limited single-agent activity, but frequent CR without MRD when combined with purine analog, albeit with chemotherapy toxicities. The anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox can achieve MRD-negative CR in multiply relapsed HCL without chemotherapy toxicities and was FDA approved in 2018 as Lumoxiti. Investigational oral non-chemotherapy options also include Vemurafenib or Dabrafenib/Trametinib targeting BRAF V600E ± MEK, and Ibrutinib targeting Bruton's tyrosine kinase.

Deciphering the genotype and phenotype of hairy cell leukemia: clues for diagnosis and treatment

Introduction: Hairy cell leukemia (HCL) is a rare, indolent B-cell neoplasm. The classical variant of the disease is characterized by the BRAF V600E mutation, which is present in virtually all cases. How this mutation leads to the signs and symptoms of the disease is currently not known. Areas covered: This review explores the genetic background of HCL, especially the BRAF V600E driver mutation, but passenger mutations and their effects are also included. The clinical significance of BRAF mutations in other cancer types is discussed, as well as BRAF- induced senescence. An overview of the major forms of treatment of HCL (cytostatic drugs, specific BRAF inhibitors, B cell-specific antibodies) is given. Finally, possible mechanisms of the monocytopenia and hairy morphology so typical of this disease are discussed. Expert opinion: Although being a rare disease, HCL and its pathogenesis can yield important information about BRAF-related cancer metabolism. Many aspects of the disease are still unclear, but with the right resources, this could change. This can lead to a more efficient and specific treatment, thus leading to decreased morbidity.

BRAF in the cross-hairs

INTRODUCTION

Hairy cell leukemia (HCL) is a rare, chronic B-cell lymphoproliferative disorder characterized by distinctive morphologic features and an indolent clinical course. The discovery of a recurrent activating mutation in BRAF (BRAF V600E) as a disease-defining genetic event in HCL has substantial diagnostic and therapeutic implications. Areas covered: Herein the authors review the role of BRAF V600E and RAF-MEK-ERK signaling in the pathogenesis of HCL, anecdotal clinical reports of BRAF inhibitor monotherapy in management of relapsed or refractory HCL, larger phase 2 trials investigating efficacy of BRAF inhibitor therapy for HCL, adverse effects commonly associated with BRAF inhibitor therapy, including cutaneous toxicity, and mechanisms of therapeutic resistance. 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.

Clinicopathologic and molecular features in hairy cell leukemia-variant: single institutional experience

Hairy cell leukemia-variant is rare. Only a small number of cases have been reported in the literature with little cytogenetic or molecular data available. In this study, we describe the clinicopathologic and genetic features of 23 patients with hairy cell leukemia-variant (16 men and 7 women) with a median age of 70 years. Most patients had splenomegaly (90%), leukocytosis (77%), and lymphocytosis (82%); no patients had monocytopenia. Histologically, the bone marrow biopsy specimens showed a mixed pattern of predominantly interstitial and lesser intrasinusoidal infiltration by leukemic cells. In bone marrow aspirate smears most cells had villous cytoplasmic features and a small nucleolus. We describe unusual sites of hairy cell leukemia-variant involvement in 4 patients, including brain, omentum, terminal ileum, and skin at the time of initial presentation. Immunophenotyping showed monotypic B-cells positive for pan B-cell antigens, CD11c, and CD103, and negative for CD25 and annexin A1. Conventional cytogenetic or fluorescence in situ hybridization analysis showed deletions of 17p13/TP53 and 11q22/ATM gene in 5/12 (42%) and 2/9 (22%) cases, respectively. Sequencing of the variable region of IGVH showed mutations (>2% deviation from germline) in 40% of the cases assessed. MAP2K1 mutation (p.C121S) was seen in 1 of 14 (7%) patients tested. No BRAF V600E mutations were detected. The patients were treated in a heterogeneous manner, but most often with therapies designed for classical hairy cell leukemia and the 5-year overall survival was 84%. In summary, hairy cell leukemia-variant exhibits a heterogeneous spectrum of clinical, morphologic, immunophenotypic, and genetic features that may overlap with classic hairy cell leukemia and other hairy cell-like B-cell neoplasms. A subset of patients can have an aggressive clinical course. In our experience MAP2K1 mutations are uncommon in this disease.

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.

The relative utilities of genome-wide, gene panel, and individual gene sequencing in clinical practice

Advances in technology that have transpired over the past 2 decades have enabled the analysis of cancer samples for genomic alterations to understand their biologic function and to translate that knowledge into clinical practice. With the power to analyze entire genomes in a clinically relevant time frame and with manageable costs comes the question of whether we ought to and when. This review focuses on the relative merits of 3 approaches to molecular diagnostics in hematologic malignancies: indication-specific single gene assays, gene panel assays that test for genes selected for their roles in cancer, and genome-wide assays that broadly analyze the tumor exomes or genomes. After addressing these in general terms, we review specific use cases in myeloid and lymphoid malignancies to highlight the utility of single gene testing and/or larger panels.

Mutations of MAP2K1 are frequent in pediatric-type follicular lymphoma and result in ERK pathway activation

Pediatric-type follicular lymphoma (PTFL) is a B-cell lymphoma with distinctive clinicopathological features. Recently, recurrent genetic alterations of potential importance for its pathogenesis that disrupt pathways associated with the germinal center reaction (TNFRSF14, IRF8), immune escape (TNFRSF14), and anti-apoptosis (MAP2K1) have been described. In an attempt to shed more light onto the pathogenesis of PTFL, an integrative analysis of these mutations was undertaken in a large cohort of 43 cases previously characterized by targeted next-generation sequencing and copy number array. Mutations in MAP2K1 were found in 49% (20/41) of the cases, second in frequency to TNFRSF14 alterations (22/41; 54%), and all together were present in 81% of the cases. Immunohistochemical analysis of the MAP2K1 downstream target extracellular signal-regulated kinase demonstrated its phosphorylation in the evaluable cases and revealed a good correlation with the allelic frequency of the MAP2K1 mutation. The IRF8 p.K66R mutation was present in 15% (6/39) of the cases and was concomitant with TNFRSF14 mutations in 4 cases. This hot spot seems to be highly characteristic for PTFL. In conclusion, TNFRSF14 and MAP2K1 mutations are the most frequent genetic alterations found in PTFL and occur independently in most cases, suggesting that both mutations might play an important role in PTFL lymphomagenesis.

Molecular Testing of Lymphoproliferative Disorders: Current Status and Perspectives

Molecular pathologic testing plays an important role for the diagnosis, prognostication and decision of treatment strategy in lymphoproliferative disease. Here, we briefly review the molecular tests currently used for lymphoproliferative disease and those which will be implicated in clinical practice in the near future. Specifically, this guideline addresses the clonality test for B- and T-cell proliferative lesions, molecular cytogenetic tests for malignant lymphoma, determination of cell-of-origin in diffuse large B-cell lymphoma, and molecular genetic alterations incorporated in the 2016 revision of the World Health Organization classification of lymphoid neoplasms. Finally, a new perspective on the next-generation sequencing for diagnostic, prognostic, and therapeutic purpose in malignant lymphoma will be summarized.

Institutional implementation of clinical tumor profiling on an unselected cancer population

BACKGROUND. Comprehensive genomic profiling of a patient's cancer can be used to diagnose, monitor, and recommend treatment. Clinical implementation of tumor profiling in an enterprise-wide, unselected cancer patient population has yet to be reported. METHODS. We deployed a hybrid-capture and massively parallel sequencing assay (OncoPanel) for all adult and pediatric patients at our combined cancer centers. Results were categorized by pathologists based on actionability. We report the results for the first 3,727 patients tested. RESULTS. Our cohort consists of cancer patients unrestricted by disease site or stage. Across all consented patients, half had sufficient and available (>20% tumor) material for profiling; once specimens were received in the laboratory for pathology review, 73% were scored as adequate for genomic testing. When sufficient DNA was obtained, OncoPanel yielded a result in 96% of cases. 73% of patients harbored an actionable or informative alteration; only 19% of these represented a current standard of care for therapeutic stratification. The findings recapitulate those of previous studies of common cancers but also identify alterations, including in AXL and EGFR, associated with response to targeted therapies. In rare cancers, potentially actionable alterations suggest the utility of a "cancer-agnostic" approach in genomic profiling. Retrospective analyses uncovered contextual genomic features that may inform therapeutic response and examples where diagnoses revised by genomic profiling markedly changed clinical management. CONCLUSIONS. Broad sequencing-based testing deployed across an unselected cancer cohort is feasible. Genomic results may alter management in diverse scenarios; however, additional barriers must be overcome to enable precision cancer medicine on a large scale. FUNDING. This work was supported by DFCI, BWH, and the National Cancer Institute (5R33CA155554 and 5K23CA157631).

The Droplet Digital PCR: A New Valid Molecular Approach for the Assessment of B-RAF V600E Mutation in Hairy Cell Leukemia

Hairy cell leukemia (HCL) is a chronic lymphoproliferative B-cell disorder where the B-RAF V600E mutation has been recently detected, as reported for solid neoplasias but not for other B-cell lymphomas. The digital droplet PCR (dd-PCR) is a molecular technique that, without standard references, is able to accurately quantitate DNA mutations. ddPCR could be an useful instrument for the detection of the B-RAF V600E mutation in HCL, where the minimal residual disease monitoring is fundamental for planning a patients-targeted treatment in the era of new anti-CD20 and anti-RAF compounds. This retrospective study enrolled 47 patients observed at the Hematology Unit of the University of Pisa, Italy, from January 2005 to January 2014: 27 patients were affected by “classic” HCL, two by the variant HCL (vHCL), and 18 by splenic marginal zone lymphoma (SMZL). The aim of the study was to compare dd-PCR to “classic” quantitative PCR (QT-PCR) in terms of sensitivity and specificity and to demonstrate its possible use in HCL. Results showed that: (1) the sensitivity of dd-PCR is about half a logarithm superior to QT-PCR (5 × 10^-5 vs. 2.5 × 10^-4), (2) the specificity of the dd-PCR is comparable to QT-PCR (no patient with marginal splenic lymphoma or HCL variant resulted mutated), (3) its high sensitivity would allow to use dd-PCR in the monitoring of MRD. At the end of treatment, among patients in complete remission, 33% were still MRD-positive by dd-PCR versus 28% by QT-PCR versus 11% by the evaluation of the B-cell clonality, after 12 months, dd-PCR was comparable to QT-PCR and both detected the B-RAF mutation in 15% of cases defined as MRD-negative by IgH rearrangement. Moreover, (4) the feasibility and the costs of dd-PCR are comparable to those of QT-PCR. In conclusion, our study supports the introduction of dd-PCR in the scenario of HCL, also during the follow-up.