Hairy cell leukemia: Uncommon clinical features, unusual sites of involvement and some rare associations

Recommendations for the Management of Patients with Hairy-Cell Leukemia and Hairy-Cell Leukemia-like Disorders: A Work by French-Speaking Experts and French Innovative Leukemia Organization (FILO) Group

INTRODUCTION

Hairy-cell leukemia (HCL) is a rare B-cell chronic lymphoproliferative disorder (B-CLPD), whose favorable prognosis has changed with the use of purine nucleoside analogs (PNAs), such as cladribine (CDA) or pentostatin (P). However, some patients eventually relapse and over time HCL becomes resistant to chemotherapy. Many discoveries have been made in the pathophysiology of HCL during the last decade, especially in genomics, with the identification of the BRAFV600E mutation and cellular biology, including the importance of signaling pathways as well as tumor microenvironment. All of these new developments led to targeted treatments, especially BRAF inhibitors (BRAFis), MEK inhibitors (MEKis), Bruton's tyrosine kinase (BTK) inhibitors (BTKis) and recombinant anti-CD22 immunoconjugates.

RESULTS

The following major changes or additions were introduced in these updated guidelines: the clinical relevance of the changes in the classification of splenic B-cell lymphomas and leukemias; the increasingly important diagnostic role of BRAFV600E mutation; and the prognostic role of the immunoglobulin (IG) variable (V) heavy chain (H) (IGHV) mutational status and repertory. We also wish to insist on the specific involvement of bones, skin, brain and/or cerebrospinal fluid (CSF) of the disease at diagnosis or during the follow-up, the novel targeted drugs (BRAFi and MEKi) used for HCL treatment, and the increasing role of minimal residual disease (MRD) assessment.

CONCLUSION

Here we present recommendations for the diagnosis of HCL, treatment in first line and in relapsed/refractory patients as well as for HCL-like disorders including HCL variant (HCL-V)/splenic B-cell lymphomas/leukemias with prominent nucleoli (SBLPN) and splenic diffuse red pulp lymphoma (SDRPL).

Hairy cell leukemia with isolated bone lesions

Key Clinical Message

¹⁸F-FDG PET/CT has clinical relevance in HCL at diagnosis and for the follow-up of patients treated, especially in case of atypical presentations such as bone involvements (which are probably underestimated) and poor bone marrow infiltration.

Abstract

Bone lesions are rarely reported in Hairy Cell Leukemia (HCL). We report two BRAF^V600E mutated HCL patients presented bone lesions at foreground, poor bone marrow involvement, and the important role ¹⁸F-FDG PET/CT played in their management. We discuss the crucial role that ¹⁸F-FDG PET/CT could play in HCL routine practice.

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.

How I treat refractory/relapsed hairy cell leukemia with BRAF inhibitors

Hairy cell leukemia (HCL) responds very well to frontline chemotherapy with purine analogs (cladribine and pentostatine). However, approximately half of patients experience 1 or more relapses, which become progressively resistant to these myelotoxic and immunosuppressive agents. At progression, standard therapeutic options include a second course of purine analogs alone or in combination with rituximab and, upon second relapse, therapy with the anti-CD22 immunotoxin moxetumomab pasudotox. Furthermore, blockade of the mutant BRAF-V600E kinase (the pathogenetic hallmark of HCL) through orally available specific inhibitors (vemurafenib or dabrafenib) effaces the peculiar morphologic, phenotypic, and molecular identity of this disease and its typical antiapoptotic behavior and is emerging as an attractive chemotherapy-free strategy in various clinical scenarios. These include patients with, or at risk of, severe infections and, in a highly effective combination with rituximab, patients with relapsed or refractory HCL. Other treatments explored in clinical trials are BTK inhibition with ibrutinib and co-inhibition of BRAF (through dabrafenib or vemurafenib) and its downstream target MEK (through trametinib or cobimetinib). Here, we focus on our experience with BRAF inhibitors in clinical trials and as off-label use in routine practice by presenting 3 challenging clinical cases to illustrate their management in the context of all available treatment options.

Hairy cell leukemia: a brief update on current knowledge and treatment prospects

PURPOSE OF REVIEW

This article provides a brief update on the recommended diagnosis and treatment strategies for patients with the classic form of hairy cell leukemia (HCL) and HCL variant (HCLv).

RECENT FINDINGS

HCL is a chronic B-cell malignancy with multiple treatment options. In recent years, many novel drugs have been assessed for HCL treatment with promising results. The investigated nonchemotherapy options include moxetumomab pasudotox, which targets CD22; vemurafenib or dabrafenib, which target the BRAFV600E protein; trametinib, which targets mitogen-activated protein kinase enzyme; and ibrutinib, which targets Bruton tyrosine kinase.

SUMMARY

Purine analogs significantly improve survival in patients with HCL. However, patients often relapse, require multiple treatments, and may become refractory. The introduction of novel agents has expanded the spectrum of therapy possibilities in those patients. In the coming years, they will assist standard therapy for patients with HCL who may currently have suboptimal results.

Analysis of a cohort of 279 patients with hairy-cell leukemia (HCL): 10 years of follow-up

In total, 279 patients with hairy-cell leukemia (HCL) were analyzed, with a median follow-up of 10 years. Data were collected up to June 2018. We analyzed responses to treatment, relapses, survival, and the occurrence of second malignancies during follow-up. The median age was 59 years. In total, 208 patients (75%) were treated with purine analogs (PNAs), either cladribine (159) or pentosatin (49), as the first-line therapy. After a median follow-up of 127 months, the median overall survival was 27 years, and the median relapse-free survival (RFS) was 11 years. The cumulative 10-year relapse incidence was 39%. In patients receiving second-line therapy, the median RFS was 7 years. For the second-line therapy, using the same or another PNA was equivalent. We identified 68 second malignancies in 59 patients: 49 solid cancers and 19 hematological malignancies. The 10-year cumulative incidences of cancers, solid tumors, and hematological malignancies were 15%, 11%, and 5.0%, respectively, and the standardized incidence ratios were 2.22, 1.81, and 6.67, respectively. In multivariate analysis, PNA was not a risk factor for second malignancies. HCL patients have a good long-term prognosis. PNAs are the first-line treatment. HCL patients require long-term follow-up because of their relatively increased risk of second malignancies.

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.

Morphological and immunophenotypical features of hairy cell leukaemia involving lymph nodes and extranodal tissues

AIMS

Hairy cell leukaemia (HCL) is a rare B cell neoplasm that mainly affects bone marrow (BM), peripheral blood (PB) and spleen. Involvement of lymph nodes and extranodal structures is considered infrequent. Herein we describe our institutional experience of nodal (n = 10) and extranodal (n = 3) HCL during a 30-year period.

METHODS AND RESULTS

Ten patients had prior evidence of HCL within the BM or PB at a median 35.8 months before nodal/extranodal diagnosis (range: <1-175 months), and HCL was diagnosed concurrently within the bone marrow of one additional patient. Nodal involvement showed distinct architectural patterns, including diffuse (62% of cases), sinusoidal (25%) and nodular (13%). Extranodal involvement was characterized as diffuse infiltration through underlying structures in all cases. Morphological features ranged from classic 'fried-egg' cytology to a plasmacytoid appearance. Nodal/extranodal disease showed an overlapping immunophenotypical profile with other small B cell lymphomas, including expression of cyclin D1 (70%), CD43 (55%), CD10 (38%) and CD5 (8%). Rates of both CD43 and CD10 reactivity were higher than described previously in leukaemic HCL, suggesting that expression may be enriched in cases with extramedullary extension.

CONCLUSIONS

Although uncommon, HCL should be considered in the differential diagnosis of small B cell neoplasms involving nodal/extranodal sites, given the therapeutic implications. In particular, recent discoveries including detection of the BRAF^V600E mutation in nearly all cases of HCL and the availability of an antibody to CD103 for use in paraffin-embedded tissues will facilitate the distinction of HCL from other small B cell lymphomas in the nodal/extranodal setting.