The genomic landscape and clonal evolutionary trajectory of classical hairy cell leukemia

The role of the JunD-RhoH axis in the pathogenesis of hairy cell leukemia and its ability to identify existing therapeutics that could be repurposed to treat relapsed or refractory disease

Hairy cell leukemia (HCL) is an indolent malignancy of mature B-lymphocytes. While existing front-line therapies achieve excellent initial results, a significant number of patients relapse and become increasingly treatment resistant. A major molecular driver of HCL is aberrant interlocking expression of the transcription factor JunD and the intracellular signaling molecule RhoH. Here we discuss the molecular basis of how the JunD-RhoH axis contributes to HCL pathogenesis. We also discuss how leveraging the JunD-RhoH axis identifies CD23, CD38, CD66a, CD115, CD269, integrin β7, and MET as new potential therapeutic targets. Critically, preclinical studies have already demonstrated that targeting CD38 with isatuximab effectively treats preexisiting HCL. Isatuximab and therapeutics directed against each of the other six new HCL targets are currently in clinical use to treat other disorders. Consequently, leveraging the JunD-RhoH axis has identified a battery of therapies that could be repurposed as new means of treating relapsed or refractory HCL.

[Updates on hairy cell leukemia (HCL) and HCL-like disorders]

Hairy cell proliferations represent very different entities. They include hairy cell leukemia in its classic form (HCL), a well-defined entity, but also the variant form of HCL (LT-V ou HCL-V), whose presentation is far from HCL and whose prognosis is poorer. Other hairy cell proliferations include splenic red pulp lymphoma (SDRPL) and splenic marginal zone lymphomas (SMZL) with circulating villous cells. In this article, we emphasize the novelties concerning the different recent biological aspects of HCL, including the unusual clinical presentations but also the importance for the diagnosis of the detection of the BRAFV600E mutation, a molecular marker of the disease, and the presence of other non-canonical mutations that should be identified because of the contraindication to the use of BRAF inhibitors. Finally, the presence of a non-mutated profile of immunoglobulin heavy chains (IGHV), observed in 20% of cases, is associated with a poor prognosis. We also provide guidance in characterizing other hairy cell proliferations when examining the blood smear. The first-line treatment of HCL has recently changed and immunochemotherapy combining cladribine plus rituximab has become the gold standard. In relapsed or refractory forms, other treatments should be discussed in a multidisciplinary consultation meeting and combine BRAF inhibitors with anti-CD20 antibodies, BTK inhibitors or Bcl-2 inhibitors. The choices should be discussed according to the patient's profile but also their biological profile.

Development of Epigenetic Modifiers with Therapeutic Potential in FMS-Related Tyrosine Kinase 3/Internal Tandem Duplication (FLT3/ITD) Acute Myeloid Leukemia and Other Blood Malignancies

Blood cancers encompass a group of diseases affecting the blood, bone marrow, or lymphatic system, representing the fourth most commonly diagnosed cancer worldwide. Leukemias are characterized by the dysregulated proliferation of myeloid and lymphoid cells with different rates of progression (acute or chronic). Among the chronic forms, hairy cell leukemia (HCL) is a rare disease, and no drugs have been approved to date. However, acute myeloid leukemia (AML) is one of the most aggressive malignancies, with a low survival rate, especially in cases with FLT3-ITD mutations. Epigenetic modifications have emerged as promising strategies for the treatment of blood cancers. Epigenetic modulators, such as histone deacetylase (HDAC) inhibitors, are increasingly used for targeted cancer therapy. New hydroxamic acid derivatives, preferentially inhibiting HDAC6 (5a-q), were developed and their efficacy was investigated in different blood cancers, including multiple myeloma (MM), HCL, and AML, pointing out their pro-apoptotic effect as the mechanism of cell death. Among the inhibitors described, 5c, 5g, and 5h were able to rescue the hematopoietic phenotype in vivo using the FLT3-ITD zebrafish model of AML. 5c (leuxinostat) proved its efficacy in cells from FLT3-ITD AML patients, promoting marked acetylation of α-tubulin compared to histone H3, thereby confirming HDAC6 as a preferential target for this new class of hydroxamic acid derivatives at the tested doses.

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 2024: Update on diagnosis, risk-stratification, and treatment-Annual updates in hematological malignancies

DISEASE OVERVIEW

Hairy cell leukemia (HCL) and HCL-like disorders, including HCL variant (HCL-V) and splenic diffuse red pulp lymphoma (SDRPL), are a very heterogenous group of mature lymphoid B-cell disorders characterized by the identification of hairy cells, a specific genetic profile, a different clinical course and the need for appropriate treatment.

DIAGNOSIS

Diagnosis of HCL is based on morphological evidence of hairy cells, an HCL immunologic score of 3 or 4 based on the CD11c, CD103, CD123, and CD25 expression, the trephine biopsy which makes it possible to specify the degree of tumoral bone marrow infiltration and the presence of BRAFV600E somatic mutation.

RISK STRATIFICATION

Progression of patients with HCL is based on a large splenomegaly, leukocytosis, a high number of hairy cells in the peripheral blood, and the immunoglobulin heavy chain variable region gene mutational status. VH4-34 positive HCL cases are associated with a poor prognosis, as well as HCL with TP53 mutations and HCL-V.

TREATMENT

Patients should be treated only if HCL is symptomatic. Chemotherapy with risk-adapted therapy purine analogs (PNAs) are indicated in first-line HCL patients. The use of chemo-immunotherapy combining cladribine (CDA) and rituximab (R) represents an increasingly used therapeutic approach. Management of relapsed/refractory disease is based on the use of BRAF inhibitors (BRAFi) plus R, MEK inhibitors (MEKi), recombinant immunoconjugates targeting CD22, Bruton tyrosine kinase inhibitors (BTKi), and Bcl-2 inhibitors (Bcl-2i). However, the optimal sequence of the different treatments remains to be determined.

Untangling hairy cell leukaemia (HCL) variant and other HCL-like disorders: Diagnosis and treatment

The variant form of hairy cell leukaemia (HCL-V) is a rare disease very different from hairy cell leukaemia (HCL), which is a very well-defined entity. The 5th WHO edition (Leukemia, 36, 2022 and 1720) classification (WHO-HAEM5) introduced splenic lymphomas/leukaemias including four different entities: (1) HCL, (2) splenic marginal zone lymphoma (SMZL) with circulating villous cells in the peripheral blood, (3) splenic lymphoma with prominent nucleolus (SLPN), which replaced HCL-V and CD5 negative B-prolymphocytic leukaemia (B-PLL), and (4) splenic diffuse red pulp lymphoma (SDRPL). All these entities have to be distinguished because of a different clinical course and the need for a different treatment. The diagnosis can be challenging because of complex cases and overlap and/or grey zones between all the entities and needs integrating clinical, histologic, immunophenotypic, cytogenetic and molecular data. We review the diagnostic criteria including clinical, immunophenotypic and molecular characteristics of patients with HCL-V and other HCL-like disorders including HCL, SDRPL, SMZL, B-PLL and the Japanese form of HCL. We also discuss the different criteria allowing us to separate these different entities and we will update the recent therapeutic options that have emerged, in particular the advances with chemoimmunotherapy and/or targeted therapies.