How I treat hairy cell leukemia

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).

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.

Single agent vemurafenib or rituximab-vemurafenib combination for the treatment of relapsed/refractory hairy cell leukemia, a multicenter experience

BACKGROUND

Hairy cell leukemia (HCL) is a rare mature B-cell malignancy that is primarily treated with purine analogues. However, relapse remains a significant challenge, prompting the search for alternative therapies. The BRAF V600E mutation prevalent in HCL patients provides a target for treatment with vemurafenib.

PATIENTS AND METHODS

This multicenter retrospective study included nine patients with relapsed/refractory (R/R) HCL from six different centers. Patient data included demographics, prior treatments, clinical outcomes, and adverse events.

RESULTS

Patients received different treatment regimens between centers, including vemurafenib alone or in combination with rituximab. Despite the differences in protocols, all patients achieved at least a partial response, with seven patients achieving a complete response. Adverse events were generally mild with manageable side effects. The absence of myelotoxic effects and manageable side effects make BRAF inhibitors attractive, especially for patients ineligible for purine analogues or those with severe neutropenia.

CONCLUSION

Single agent vemurafenib or in combination with rituximab appears to be a promising therapeutic option for R/R HCL. Further research is needed to establish standardized treatment protocols and to investigate long-term outcomes.

Vemurafenib and Obinutuzumab as Frontline Therapy for Hairy Cell Leukemia

BACKGROUND: Hairy cell leukemia (HCL) is characterized by the underlying genetic lesion of BRAFV600E and responsiveness to BRAF inhibitors. We assessed the safety and activity of the BRAF inhibitor vemurafenib combined with obinutuzumab in patients with previously untreated HCL. METHODS: We conducted a single-arm, multicenter clinical study of vemurafenib plus obinutuzumab. Vemurafenib 960 mg twice daily was administered for four cycles, and obinutuzumab was administered in cycles 2 to 4. The primary end point was complete remission (CR). Secondary end points included assessment of safety, minimal residual disease (MRD), and BRAF allele burden according to digital droplet polymerase chain reaction (ddPCR). RESULTS: Thirty patients were enrolled in the study, and 27 patients completed all four cycles of treatments and achieved CR (90%; 95% confidence interval [CI], 73 to 98). Three patients discontinued the study early because of adverse events and were not evaluable for response. Of the 27 patients who achieved CR, 26 patients (96%; 95% CI, 81 to 99) achieved MRD negativity. BRAFV600E allele was undetectable by ddPCR in all 21 evaluable patients. At a median follow-up of 34.9 months (95% CI, 29.6 to 36.9), no patient experienced disease relapse. The most common vemurafenib-related adverse events were rash and arthralgia. Febrile neutropenia occurred in two patients, and blood or platelet transfusions were required in two patients. CONCLUSIONS: Combined time-limited vemurafenib and obinutuzumab achieved CR in more than 90% of patients with previously untreated HCL. In this small study, acquired vemurafenib resistance or dose-limiting toxicity was not observed. Patients were not observed long enough to reveal secondary malignancies. (Funded by the National Cancer Institute and others; ClinicalTrials.gov number, NCT03410875.)

Repurposable Drugs for Immunotherapy and Strategies to Find Candidate Drugs

Conventional drug discovery involves significant steps, time, and expenses; therefore, novel methods for drug discovery remain unmet, particularly for patients with intractable diseases. For this purpose, the drug repurposing method has been recently used to search for new therapeutic agents. Repurposed drugs are mostly previously approved drugs, which were carefully tested for their efficacy for other diseases and had their safety for the human body confirmed following careful pre-clinical trials, clinical trials, and post-marketing surveillance. Therefore, using these approved drugs for other diseases that cannot be treated using conventional therapeutic methods could save time and economic costs for testing their clinical applicability. In this review, we have summarized the methods for identifying repurposable drugs focusing on immunotherapy.

Long-term outcomes in patients with relapsed or refractory hairy cell leukemia treated with vemurafenib monotherapy

Vemurafenib, an oral BRAF inhibitor, has demonstrated high response rates in relapsed/refractory (R/R) hairy cell leukemia (HCL). However, little is known about long-term outcomes and response to retreatment. Herein, we report the results of 36 patients with R/R HCL treated with vemurafenib from the United States arm of the phase 2 clinical trial (NCT01711632). The best overall response rate was 86%, including 33% complete response (CR) and 53% partial response (PR). After a median follow-up of 40 months, 21 of 31 responders (68%) experienced relapse with a median relapse-free survival (RFS) of 19 months (range, 12.5-53.9 months). There was no significant difference in the RFS for patients with CR vs PR. Fourteen of 21 (67%) relapsed patients were retreated with vemurafenib, with 86% achieving complete hematologic response. Two patients acquired resistance to vemurafenib with the emergence of new KRAS and CDKN2A mutations, respectively. Six of 12 (50%) responders to vemurafenib retreatment experienced another relapse with a median RFS of 12.7 months. Overall survival (OS) was 82% at 4 years, with a significantly shorter OS in patients who relapsed within 1 year of initial treatment with vemurafenib. Higher cumulative doses or a longer duration of treatment did not lengthen the durability of response. All adverse events in the retreatment cohort were grade 1/2 except for 1 case of a grade 3 rash and 1 grade 3 fever/pneumonia. Our data suggest that vemurafenib retreatment is a safe and effective option for patients with R/R HCL.

Patient-driven research: Initial results from a prospective health-related quality of life study performed at the request of patients living with hairy cell leukemia

A diagnosis of leukemia can have a profound effect on patients' health-related quality of life (HRQoL), however this has not been measured prospectively in patients with hairy cell leukemia (HCL). At the request of patients living with HCL who had identified this gap in knowledge about the disease, we conducted a longitudinal study of HRQoL among patients enrolled in the HCL Patient Data Registry (PDR). From September 1, 2018 to September 1, 2020, 165 patients were enrolled in the study and completed the baseline survey. The Functional Assessment of Cancer Therapy - Leukemia (FACT-Leu) was used to measure patients' HRQoL. Results show that newly diagnosed HCL patients reported the lowest HRQoL, followed by patients in relapse and those on "watch and wait." Factors associated with higher (better) FACT-Leu total scores in the multivariable analysis included older age, higher social support, and greater physical activity. These same factors were associated with lower levels of fatigue. In rare diseases where it is difficult to perform large prospective studies, patient/researcher collaborations are critical for the identification of studies that are of importance to patients and their families in order to maximize the benefits of the research and improve the lives of patients living with HCL.

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.

Treatment of Classic Hairy Cell Leukemia: Targeting Minimal Residual Disease beyond Cladribine

Simple Summary

Standard treatment with purine analogues facilitates a near normal life expectancy in the majority of patients with classic hairy cell leukemia (HCL), a rare chronic B-cell malignancy. However, nearly all patients ultimately relapse and require retreatment, while drug-induced myelotoxicity accumulates predisposing to infectious complications and, possibly, secondary malignancies. Persistence of minimal residual disease (MRD) in a substantial portion of treated patients has become a surrogate for this still limited treatment efficacy. New insights into disease biology initiated design and investigation of several new, chemotherapy-free, targeted drugs with encouraging efficacy in early clinical trials aimed at enhancing eradication of MRD and optimizing drug tolerability. This review provides an update on recent clinical trials investigating treatment strategies beyond purine analogues in HCL and discusses clinically relevant obstacles still to overcome.

Abstract

Classic hairy cell leukemia (HCL) is a rare indolent B-cell lymphoproliferative disorder characterized by profound pancytopenia and frequent infectious complications due to progressive infiltration of the bone marrow and spleen. Lacking effective treatment options, affected patients were confronted with a dismal survival prognosis of less than 5 years when the disease was first described in 1958. Tremendous therapeutic advances were accomplished with the introduction of purine analogues such as cladribine in the 1990s, facilitating a near-normal life expectancy in most HCL patients. Nevertheless, nearly all patients eventually relapse and require successive retreatments, while drug-associated myelotoxicity may accumulate and secondary malignancies may evolve. Detection of minimal residual disease (MRD) in a substantial portion of treated patients has become a surrogate for this still limited treatment efficacy. In the last decade, novel biologic insights such as identification of the driver mutation BRAF V600E have initiated the development and clinical investigation of new, chemotherapy-free, targeted drugs in HCL treatment, with encouraging efficacy in early clinical trials aimed at boosting eradication of MRD while optimizing drug tolerability. This review summarizes current clinical trials investigating treatment strategies beyond purine analogues in HCL and discusses clinically relevant obstacles still to overcome.

CD5-Negative, CD10-Negative Low-Grade B-Cell Lymphoproliferative Disorders of the Spleen

CD5-negative, CD10-negative low-grade B-cell lymphoproliferative disorders (CD5-CD10-LPD) of the spleen comprise a fascinating group of indolent, neoplastic, mature B-cell proliferations that are essential to accurately identify but can be difficult to diagnose. They comprise the majority of B-cell LPDs primary to the spleen, commonly presenting with splenomegaly and co-involvement of peripheral blood and bone marrow, but with little to no involvement of lymph nodes. Splenic marginal zone lymphoma is one of the prototypical, best studied, and most frequently encountered CD5-CD10-LPD of the spleen and typically involves white pulp. In contrast, hairy cell leukemia, another well-studied CD5-CD10-LPD of the spleen, involves red pulp, as do the two less common entities comprising so-called splenic B-cell lymphoma/leukemia unclassifiable: splenic diffuse red pulp small B-cell lymphoma and hairy cell leukemia variant. Although not always encountered in the spleen, lymphoplasmacytic lymphoma, a B-cell lymphoproliferative disorder consisting of a dual population of both clonal B-cells and plasma cells and the frequent presence of the MYD88 L265P mutation, is another CD5-CD10-LPD that can be seen in the spleen. Distinction of these different entities is possible through careful evaluation of morphologic, immunophenotypic, cytogenetic, and molecular features, as well as peripheral blood and bone marrow specimens. A firm understanding of this group of low-grade B-cell lymphoproliferative disorders is necessary for accurate diagnosis leading to optimal patient management.

Vemurafenib plus Rituximab in Refractory or Relapsed Hairy-Cell Leukemia

BACKGROUND

Hairy-cell leukemia (HCL) is a CD20+ indolent B-cell cancer in which a BRAF V600E kinase-activating mutation plays a pathogenetic role. In clinical trials involving patients with refractory or relapsed HCL, the targeting of BRAF V600E with the oral BRAF inhibitor vemurafenib led to a response in 91% of the patients; 35% of the patients had a complete response. However, the median relapse-free survival was only 9 months after treatment was stopped.

METHODS

In a phase 2, single-center, academic trial involving patients with refractory or relapsed HCL, we assessed the safety and efficacy of vemurafenib (960 mg, administered twice daily for 8 weeks) plus concurrent and sequential rituximab (375 mg per square meter of body-surface area, administered for 8 doses over a period of 18 weeks). The primary end point was a complete response at the end of planned treatment.

RESULTS

Among the 30 enrolled patients with HCL, the median number of previous therapies was 3. A complete response was observed in 26 patients (87%) in the intention-to-treat population. All the patients who had HCL that had been refractory to chemotherapy (10 patients) or rituximab (5) and all those who had previously been treated with BRAF inhibitors (7) had a complete response. Thrombocytopenia resolved after a median of 2 weeks, and neutropenia after a median of 4 weeks. Of the 26 patients with a complete response, 17 (65%) were cleared of minimal residual disease (MRD). Progression-free survival among all 30 patients was 78% at a median follow-up of 37 months; relapse-free survival among the 26 patients with a response was 85% at a median follow-up of 34 months. In post hoc analyses, MRD negativity and no previous BRAF inhibitor treatment correlated with longer relapse-free survival. Toxic effects, mostly of grade 1 or 2, were those that had previously been noted for these agents.

CONCLUSIONS

In this small study, a short, chemotherapy-free, nonmyelotoxic regimen of vemurafenib plus rituximab was associated with a durable complete response in most patients with refractory or relapsed HCL. (Funded by the European Research Council and others; HCL-PG03 EudraCT number, 2014-003046-27.).

The current role of interferon in hairy cell leukaemia: clinical and molecular aspects

We investigated the current role of interferon‐alpha (IFNα) in hairy cell leukaemia (HCL) in a retrospective analysis of patients with HCL. A cohort of 74 patients with HCL was divided in to three groups: (A) patients aged >65 years with first‐line treatment; (B) patients with comorbidities with first‐line treatment; (C) patients who were purine analogues resistant. In total, 94% achieved a response, with a complete response rate of 24%. After a median (range) follow‐up of 60 (7–236) months, 55 patients (78%) are still responding. The 5‐year progression‐free survival was 95%, 68%, and 96% in groups A, B and C respectively. A proportion of patients were monitored through their B‐Raf proto‐oncogene, serine/threonine kinase (BRAF)‐V600E status. IFNα remains a possible option in select patients with HCL, where minimal residual disease negativity is achievable.

Lytic Bone Lesion: An Unusual Presentation of Hairy Cell Leukemia

Hairy cell leukemia (HCL) is a seldom encountered malignancy of lymphocytes with a low incidence in the United States. HCL generally follows an indolent course and not all patients require treatment. Most patients are asymptomatic at the time of diagnosis. Treatment is reserved for those with anemia, thrombocytopenia, neutropenia, recurrent infections, symptomatic splenomegaly, or lymphadenopathy impairing vital organ function. Purine analogs are the mainstay of treatment with a durable response. We report a case of a 49-year old Ukrainian male who presented with bone pain secondary to a lytic bone lesion who was diagnosed with HCL.

Moxetumomab pasudotox for hairy cell leukemia: preclinical development to FDA approval

Moxetumomab pasudotox (MP) is an immunotoxin that recently received US Food and Drug Administration (FDA) approval for the treatment of hairy cell leukemia (HCL) that has failed at least 2 prior lines of therapy, including a purine analog. MP is a recombinant immunotoxin that consists of an anti-CD22 immunoglobulin variable domain genetically joined to Pseudomonas exotoxin (PE38). Unlike most antibody-drug conjugates, which use a chemical linker, recombinant DNA techniques are used to produce MP. MP and its predecessor, BL22, were initially developed to treat non-Hodgkin lymphoma, acute lymphoblastic leukemia, and HCL. However, MP was found to be particularly effective in HCL due to the high level of CD22 cell-surface expression. The recent pivotal phase 3 trial of MP in relapsed/refractory HCL demonstrated a durable complete remission rate of 30%, and 85% of complete responders achieved minimal residual disease negativity, which is associated with improved disease-free survival outcomes in HCL. In addition to an exceptional depth of response, MP appears to be less immunosuppressive than purine analogs. MP is generally well tolerated but has unique toxicities, including capillary leak syndrome and hemolytic uremic syndrome, which are poorly understood. This review will encompass the preclinical and clinical development of MP, with particular attention to its current indication in HCL.

BRAF V600E mutation detection in hairy cell leukemia-utility of archival DNA from bone marrow aspirate/imprint smear and amplification refractory mutation system

BRAF V600E is a disease defining mutation for hairy cell leukemia (HCL), which helps in its diagnosis and differentiation from morphologically similar splenic marginal zone lymphoma (SMZL) and HCL-variant (HCL-v). Forty eight cases:HCL(n = 34), SMZL(n = 11) and HCL-v(n = 3) were included. Of these, 32 were retrospective and 16 were prospective. DNA was extracted, in retrospective cases from cells obtained by smears from bone marrow aspirate/trephine imprint (BMA/BMTx) slides, and in prospective cases from peripheral blood (PB)/BMA samples. BRAF V600E mutation testing was done using ARMS-PCR. BRAF V600E mutation was positive in all HCL and negative in all SMZL and HCL-v cases. DNA extracted from BMA/BMTx slides gave results comparable to DNA extracted from PB/BMA samples. Median age of presentation for HCL (53 years) and SMZL (56 years) were quite similar, however, HCL-v (71 years) cases presented at an older age. Statistically significant differences between the three groups were seen for total leucocyte, platelet, absolute lymphocyte and monocyte counts, bone marrow-infiltration pattern, reticulin fibrosis, and an expression of CD11c, CD25, CD103, CD123, and CD200. The use of BMA/BMTx smears for DNA extraction was found to be a useful alternative to DNA extraction from formalin-fixed paraffin-embedded biopsy sections. ARMS-PCR is an efficient and specific technique to detect BRAF V600E mutation in HCL patients.

Adverse event rates and economic burden associated with purine nucleoside analogs in patients with hairy cell leukemia: a US population-retrospective claims analysis

Background

Purine nucleoside analogs (PNAs) are the recommended first-line treatment for patients with hairy cell leukemia (HCL), but they are associated with adverse events (AEs). Due to a lack of real-world evidence regarding AEs that are associated with PNAs, we used commercial data to assess AE rates, AE-related health care resource utilization (HCRU), and costs among PNA-treated patients with HCL. Adults aged ≥18 years with ≥2 claims for HCL ≥30 days apart from 1 January 2006 through 31 December 2015 were included. Included patients had ≥1 claim for HCL therapy (cladribine ± rituximab or pentostatin ± rituximab [index date: first claim date]) and continuous enrollment for a ≥ 6-month baseline and ≥ 12-month follow-up period. Patient sub-cohorts were based on the occurrence of myelosuppression and opportunistic infections (OIs). Generalized linear models were used to compare HCRU and costs.

Results

In total, 647 PNA-treated patients were identified (mean age: 57.1 years). Myelosuppression and OI incidence were 461 and 42 per 1000 patient-years, respectively. Adjusted results indicated that those with myelosuppression had higher rates of hospitalization (47.4% vs 12.4%; P < .0001) and incurred higher mean inpatient costs ($23,517 vs $12,729; P = .011) and total costs ($57,325 vs $34,733; P = .001) as compared with those without myelosuppression. Similarly, patients with OIs had higher rates of hospitalization (53.8% vs 30.8%; P = .025) and incurred higher mean inpatient costs ($21,494 vs $11,229; P < .0001) as compared with those without OIs.

Conclusions

PNA therapy is highly effective but associated with significant toxicities that increase costs; these findings indicate a need for therapies with improved toxicity profiles and better risk stratification of patients at risk of developing myelosuppression and OIs.

Disseminated Histoplasmosis with Concurrent Hairy Cell Leukemia

Histoplasmosis is an endemic fungal infection that can lead to disseminated disease, especially in immunosuppressed patients. Hairy cell leukemia is a rare, slow-growing hematological malignancy. Concurrence of histoplasmosis and hairy cell leukemia is extremely rare. We describe a 69-year-old male who presented with fever, dry cough, pancytopenia, multiple pulmonary nodules, and massive splenomegaly. Histoplasma urinary antigen was positive and disease was confirmed by biopsy of lung lesions. Peripheral smear showed 'hairy cells', and bone marrow biopsy revealed findings of hairy cell leukemia. The patient was treated with intravenous amphotericin, followed by oral itraconazole. After the initial treatment of infection, treatment for hairy cell leukemia was started with cladribine. We will discuss the principles of treating disseminated histoplasmosis in the setting of immunosuppression, and hairy cell leukemia with coexisting infection.

Classic hairy cell leukemia complicated by pancytopenia and severe infection: a report of 3 cases treated with vemurafenib

Infections are a major cause of morbidity and mortality in HCL patients, and myelosuppressive therapies increase the risk of poor outcomes. Vemurafenib achieves rapid hematologic improvement in HCL and may facilitate management during life-threatening infection.

Retrospective Analysis of Hairy Cell Leukemia Patients Treated with Different Modalities as First Line: Real-Life Experience Over 20 years

We aimed to analyze the characteristics and response rates of different treatment modalities in hairy cell leukemia patients over 20 diagnosed as hairy cell leukemia (HCL). Clinical data, response rates and survival outcome of the patients who were diagnosed with HCL were retrospectively analyzed. Fifty-two patients with a median age of 50 (28-87) years were enrolled in the study. 38 patients (73%) were male and male to female ratio was 2.7. First line therapy was cladrabine in 36 patients (69.2%). The overall response rate was 97%. CR and PR rates were 86.1% and 11.1%, respectively. Interferon was used in 10(19.2%) patients who were diagnosed before 2000s years. CR and PR rates were 70% and 30%, respectively. Although the CR rates were lower in IFN group, this difference could not be reached statistically significance (p = 0.24). The median follow up was 48 months (12-252). The median OS was not reached and median PFS was 150 months (95% CI, 116-214). The OS at 36 and 48 months were 95.9% and 92.3%, respectively and the PFS at 36 and 48 months were 90.2% and 83.4%, respectively. After the introduction of purine analogues, the fate of the HCL patients have been changed. Cladrabin achieved very high response rates in both young and older patients, in our study. Although relapse still constitutes a problem, another single dose of cladrabine results in good response rates.

New treatment options in hairy cell leukemia with focus on BRAF inhibitors

Hairy cell leukemia (HCL) responds initially very well to chemotherapy with purine analogues. However, up to 50% of patients relapse, often multiple times, and become progressively less sensitive to these myelotoxic and immune-suppressive drugs. At progression, viable therapeutic strategies include addition of rituximab to purine analogues, and treatment with the anti-CD22 immunotoxin moxetumomab pasudotox, which has been recently approved by the FDA in HCL patients after at least two prior therapies. Identification of the BRAF-V600E kinase mutation as the genetic cause of HCL has opened the way, in the relapsed/refractory experimental setting, to targeted and non-myelotoxic effective strategies that are based on inhibition of BRAF with vemurafenib, co-inhibition of BRAF and its target MEK with dabrafenib and trametinib, and BRAF inhibition with vemurafenib combined with anti-CD20 immunotherapy. In particular, vemurafenib plus rituximab is emerging as a short, safe, chemotherapy-free regimen able to induce deep complete remissions in most HCL patients refractory to, or relapsed multiple times, after chemo(immuno)therapy.

Outcome of hairy cell leukemia patients treated with cladribine - a 10-year single-center experience in Pakistan

INTRODUCTION AND OBJECTIVE

Hairy cell leukemia is an uncommon, indolent B-cell lymphoproliferative disorder. Therapy with cladribine (2-chlorodeoxyadenosine) is able to induce complete remission (CR) in the majority of patients after a single course of treatment. We report the outcomes of patients treated at Aga Khan University Hospital, Karachi, Pakistan.

METHODS

This was a retrospective review. Medical records of patients were used to collect data.

RESULTS

A total of 21 patients with hairy cell leukemia were treated with cladribine. All patients achieved an initial CR. Four patients (19%) required hospitalization and therapy for neutropenic fever. Six patients (29%) relapsed at a median of 48 months. All 6 patients were treated for relapse, out of which 4 achieved CR, 1 had partial response and 1 had refractory disease. The overall survival rate was 90.5%, with a median follow-up of 35 months.

CONCLUSION

A single course of cladribine is able to induce CR in a vast majority of patients. Unfortunately, relapse is not uncommon. Patients who relapse can be successfully retreated with cladribine. Cladribine has impressive efficacy and a favorable acute and long-term toxicity profile when administered to patients with HCL.

[Clinical analysis of 24 patients of hairy cell leukemia treated by cladribine]

Objective: To investigate the curative effect of hairy cell leukemia by clatabine. Methods: The clinical data of 24 patients with hairy cell leukemia treated by cladribine from November 2006 to October 2017 were analyzed retrospectively, then the curative effect and adverse drug reaction were analyzed. Results: ① A total of 24 patients including 22 male and 2 female, and the median age was 49.5 years (range 33 to 76) at diagnosis. There were 20 patients with of splenomegaly (4 patients with mild splenomegaly, 4 moderate splenomegaly, and 12 massive splenomegaly), 3 patients with enlargement of lymph nodes, and 1 patients who had undergone splenectomy. Five patients were pancytopenia, 15 were cytopenia in 2 lineages, and 4 patients were cytopenia only in one lineage. The median ratio of HCL cells detected by flow cytometry in bone marrow was 21.79% (0.69%-68.96%). BRAF mutation was detected in 15 patients by first generation or next generation sequencing technology. ② Among 24 patients, 20 were treated with cladribine alone (one course in 19 patients, 2 courses in 1 patient), and 4 patients were treated with cladribine combined with rituximab (one course in 3 patients, 2 courses in 1 patient). Excepting 5 patients whose follow-up time was not reaching 6 months, 19 patients were evaluated for efficacy in 6-12 months after treatment: 9 patients obtained CR, 9 obtained unconfirmed CR (Cru), the other 1 obtained PR, the CR/CRu rate was 94.7%, the overall response rate (ORR) was 100.0%. ③ All the 24 patients appeared 2-4 grade hematological adverse reactions after cladribine treatment, which were mainly grade 3/4 neutropenia (66.67%) and grade 3/4 thrombocytopenia (29.2%). All the adverse reactions were controlled or recovered spontaneously. ④ After the median follow-up time of 15 (3-133) months, no progression, recurrence or death occurred in the patients. Both median OS and PFS were not reached. Conclusion: This study suggests that treatment of HCL with cladribine has high response rate, controllable adverse reactions and the good prognosis.

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.

Genetic convergence of rare lymphomas

PURPOSE OF REVIEW

We review the genetic foundations of different rare lymphomas to examine their shared origins. These data indicate the potential application of genomics to improve the diagnosis and treatment of these rare diseases.

RECENT FINDINGS

Next generation sequencing technologies have provided an important window into the genetic underpinnings of lymphomas. A growing body of evidence indicates that although some genetic alterations are specific to certain diseases, others are shared across different lymphomas. Many such genetic events have already demonstrated clinical utility, such as BRAF V600E that confers sensitivity to vemurafenib in patients with hairy cell leukemia.

SUMMARY

The rareness of many lymphoma subtypes makes the conduct of clinical trials and recruitment of significant numbers of patients impractical. However, a knowledge of the shared genetic origins of these rare lymphomas has the potential to inform 'basket' clinical trials in which multiple lymphoma subtypes are included. These trials would include patients based on the presence of alterations in targetable driver genes. Such approaches would be greatly strengthened by a systematic assessment of significant patient numbers from each subtype using next generation sequencing.

Interferon-alpha-based immunotherapies in the treatment of B cell-derived hematologic neoplasms in today's treat-to-target era

B cell lymphoma and multiple myeloma (MM) are the most common hematological malignancies which benefit from therapeutic monoclonal antibodies (mAbs)-based immunotherapies. Despite significant improvement on patient outcome following the use of novel therapies for the past decades, curative treatment is unavailable for the majority of patients. For example, the 5-year survival of MM is currently less than 50%. In the 1980s, interferon-α was used as monotherapy in newly diagnosed or previously treated MM with an overall response rate of 15-20%. Noticeably, a small subset of patients who responded to long-term interferon-α further achieved sustained complete remission. Since 1990, interferon-α-containing regimens have been used as a central maintenance strategy for patients with MM. However, the systemic administration of interferon-α was ultimately limited by its pronounced toxicity. To address this, the selective mAb-mediated delivery of interferon-α has been developed to enhance specific killing of MM and B-cell malignant cells. As such, targeted interferon-α therapy may improve therapeutic window and sustain responses, while further overcoming suppressive microenvironment. This review aims to reinforce the role of interferon-α by consolidating our current understanding of targeting interferon-α with tumor-specific mAbs for B cell lymphoma and myeloma.

Characteristics and treatment patterns among US patients with hairy cell leukemia: a retrospective claims analysis

AIM

Describe hairy cell leukemia (HCL) treatment patterns using a large, nationally representative US database.

PATIENTS & METHODS

Adults newly diagnosed with HCL (1 January 2006 to 30 June 2014) with continuous health plan enrollment ≥180 days pre- and 90 days post-diagnosis were identified from the QuintilesIMS PharMetrics Plus Health Plan Claims Database. Treatment patterns by line of therapy were assessed over the variable follow-up.

RESULTS

Among 749 HCL patients (77.4% male; mean age 55.6; mean 32.3 months follow-up), only 37.7% initiated first-line therapy during the available follow-up in a mean of 4.4 months following diagnosis; the majority (75.5%) received cladribine (mean duration 7.3 days). Thirty-eight patients (5.1%) received second-line treatment.

CONCLUSION

Over 2.7 years follow-up, more than a third of patients initiated first-line therapy which appeared to provide a long-lasting response.

sIL2R ratio as early marker for response in hairy cell leukemia and the prognostic relevance of IL28B genotype to interferon-α therapy

Interferon-α (IFNα) was the first effective drug therapy for hairy cell leukemia (HCL). Nowadays, it is used as an alternative treatment in selected patients. Due to unlimited treatment time, monitoring and early prediction of response are important. Moreover, IFNα is used in the therapy of chronic hepatitis C, where a single nucleotide polymorphism of interleukin-28B gene (IL28B) correlates with therapy response. The role of this polymorphism in therapy response of IFNα-treated patients with HCL is unknown. Thirty-seven HCL patients treated between 1978 and 2014 were included in this study. Treatment strategy and response parameters (blood cell counts, soluble interleukin-2 receptor (sIL2R), and bone marrow examination) have been assessed. Relative decrease of sIL2R was correlated with outcome parameters. Response parameters of IFNα-treated patients were correlated with IL28B polymorphism. Twenty-one patients were analyzed for the correlation of sIL2R ratio and outcome. After 1 and 3 months of therapy (IFNα or cladribine (CDA)), the median sIL2R level showed a relative decrease of 79 and 91%. These decreases significantly correlate with time to complete remission (CR, p = 0.029 and p = 0.018). Correlation analyses of IL28B genotype with outcome parameters are not significant. Six patients (16%) were diagnosed with secondary malignancies, and one death was registered (median follow-up time 14 years). IFNα is a safe, effective, and well-tolerated long-term treatment in HCL. Relative decreases of sIL2R levels correlate with time to CR and are useful as early predictor for response. There is no significant correlation between IL28B polymorphism and treatment response to IFNα. Graphical abstract.

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).

Consensus guidelines for the diagnosis and management of patients with classic hairy cell leukemia

Hairy cell leukemia is an uncommon hematologic malignancy characterized by pancytopenia and marked susceptibility to infection. Tremendous progress in the management of patients with this disease has resulted in high response rates and improved survival, yet relapse and an appropriate approach to re-treatment present continuing areas for research. The disease and its effective treatment are associated with immunosuppression. Because more patients are being treated with alternative programs, comparison of results will require general agreement on definitions of response, relapse, and methods of determining minimal residual disease. The development of internationally accepted, reproducible criteria is of paramount importance in evaluating and comparing clinical trials to provide optimal care. Despite the success achieved in managing these patients, continued participation in available clinical trials in the first-line and particularly in the relapse setting is highly recommended. The Hairy Cell Leukemia Foundation convened an international conference to provide common definitions and structure to guide current management. There is substantial opportunity for continued research in this disease. In addition to the importance of optimizing the prevention and management of the serious risk of infection, organized evaluations of minimal residual disease and treatment at relapse offer ample opportunities for clinical research. Finally, a scholarly evaluation of quality of life in the increasing number of survivors of this now manageable chronic illness merits further study. The development of consensus guidelines for this disease offers a framework for continued enhancement of the outcome for patients.

How I manage patients with hairy cell leukaemia

Patients with hairy cell leukaemia (HCL) have highly favourable outcomes after purine analogue therapy. However, most patients subsequently relapse and require re-treatment. A minority of patients develop purine analogue-refractory disease. Targeted therapies have improved outcomes for such patients. Recently, the BRAF V600E mutation was identified in most patients with classical HCL, resulting in constitutive mitogen-activated protein kinase pathway activation; impressive responses are achieved in heavily pre-treated patients with BRAF inhibition. The CD22-targeted immunoconjugate moxetumomab pasudotox and BTK inhibitor ibrutinib also achieve responses in relapsed and refractory patients. HCL variant and the IGHV4-34 molecular variant of HCL lack BRAF mutation and have inferior outcomes with standard purine analogue therapy. The addition of rituximab to purine analogues achieves very high rates of minimal residual disease-negative complete remission and improves outcomes for patients with HCL variant. Given the rarity of HCL, optimal integration of novel therapies into treatment algorithms will require well-designed, collaborative studies.

Leukocytoclastic vasculitis associated with hairy cell leukemia at diagnosis: a case report and review of the literature

BACKGROUND

Autoimmune manifestations may occur in patients with hairy cell leukemia (HCL), and some rare cases of polyarteritis nodosa and leukocytoclastic vasculitis have been reported. However, data regarding the treatment of these cutaneous manifestations are lacking, given the rarity of the concomitance of HCL and vasculitic syndromes.

CASE PRESENTATION

We present a 37-year-old man with paraneoplastic leukocytoclastic vasculitis complicating newly diagnosed HCL. The vasculitis completely resolved after the first 3 weekly administrations of cladribine, which is regarded as the gold-standard treatment for this disease. The underlying leukemia showed refractoriness to the same agent, thus requiring a second line of treatment.

CONCLUSIONS

The clinical picture we have observed is of interest for the following reasons: i) it confirms an existing pathogenetic relationship between this lymphoproliferative disorder and its cutaneous manifestations, as suggested by the prompt resolution of the purpuric lesions upon cladribine administration; ii) it indicates that cladribine is an effective treatment for HCL-related paraneoplastic syndromes, including leukocytoclastic vasculitis; iii) the evolution and the outcomes of the paraneoplastic manifestations may be independent of those of the underlying leukemia, which showed less than a partial response to its initial treatment.

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.

Selective Spleen Embolization of Splenomegaly to Improve Thrombocytopenia Facilitating Open Aortic Aneurysm Repair: A Staged Approach

We present an 82-year-old man with a history of hairy cell leukemia, having an 11-cm abdominal aortic aneurysm, who also had severe thrombocytopenia (about 20 000 platelets/μL) and splenomegaly at presentation. The patient had unfavorable anatomy for endovascular aneurysm repair, and therefore, an open procedure was planned. To reduce risk for perioperative bleeding and optimize patient preoperative status, a staged approach was employed. Initially, several sessions of embolization of 2 splenic artery branches were performed with the intent to decrease spleen size and to increase platelet count thus decreasing the perioperative bleeding risk. Then, after successfully increasing platelet count (280 000 PLT/μL), open repair of the aneurysm was conducted. This case demonstrates that selective splenic embolization in patients with hypersplenism and subsequent thrombocytopenia who are in need for major surgery may achieve a significant rise in platelet count and optimize patient's preoperative status in order to avoid bleeding complications.

A Unique Hairy Cell Leukemia Variant

A 65-year-old woman presented with easy bruising, left upper quadrant pain, decreased appetite, and weight loss. She had splenomegaly and lymphocytosis (lymphocyte count of 11.6 × 10(9)/l), with remarkably abnormal appearing morphology. Her hemoglobin and platelet counts were normal. Peripheral blood flow cytometry revealed a monoclonal B-cell population expressing CD11c, CD25, CD19, CD20, and CD103. An initial diagnosis of hairy cell leukemia (HCL) was made, and the patient was treated with a standard 5-day course of cladribine. However, her lymphocytosis improved transiently, with a relapse 4 months later. There was no improvement in her splenomegaly. An HCL variant (HCL-v) was considered based on her resistance to treatment with a purine nucleoside analog. A subsequent splenectomy improved symptoms. Two years after, the patient suffered a relapse and underwent 6 cycles of CHOP-R (cyclophosphamide, hydroxydaunomycin, oncovin, prednisone, and rituximab), achieving partial remission. While under observation, she progressed with lymphocytosis 6 months later and was treated with pentostatin. There was no significant improvement in her disease, and she died 8 weeks following treatment initiation. HCL-v is a clinically more aggressive mature B-cell lymphoma than HCL with worse splenomegaly, higher lymphocyte counts, and resistance to typical HCL therapy with purine nucleoside analogs. Early recognition of HCL-v in the history, physical examination, and investigations with morphology and flow cytometry is key to patient management. Further, as in our case of HCL-v, cell morphology can be distinctly atypical, with large nucleoli and extremely convoluted nuclei. The distinction between HCL and HCL-v is important as HCL-v patients require more aggressive therapy and closer follow-up.

Requisite analytic and diagnostic performance characteristics for the clinical detection of BRAF V600E in hairy cell leukemia: a comparison of 2 allele-specific PCR assays

Detection of high-frequency BRAF V600E mutations in hairy cell leukemia (HCL) has important diagnostic utility. However, the requisite analytic performance for a clinical assay to routinely detect BRAF V600E mutations in HCL has not been clearly defined. In this study, we sought to determine the level of analytic sensitivity needed for formalin-fixed, paraffin-embedded (FFPE) and frozen samples and to compare the performance of 2 allele-specific polymerase chain reaction (PCR) assays. Twenty-nine cases of classic HCL, including 22 FFPE bone marrow aspirates and 7 frozen specimens from blood or bone marrow were evaluated using a laboratory-developed allele-specific PCR assay and a commercially available allele-specific quantitative PCR assay-myT BRAF Ultra. Also included were 6 HCL variant and 40 non-HCL B-cell lymphomas. Two cases of classic HCL, 1 showing CD5 expression, were truly BRAF V600E-negative based on negative results by PCR and sequencing despite high-level leukemic involvement. Among the remaining 27 specimens, V600E mutations were detected in 88.9% (17/20 FFPE; 7/7 frozen) and 81.5% (15/20 FFPE; 7/7 frozen), for the laboratory-developed and commercial assays, respectively. No mutations were detected among the 46 non-HCL lymphomas. Both assays showed an analytic sensitivity of 0.3% involvement in frozen specimens and 5% in FFPE tissue. On the basis of these results, an assay with high analytic sensitivity is required for the clinical detection of V600E mutations in HCL specimens. Two allele-specific PCR assays performed well in both frozen and FFPE bone marrow aspirates, although detection in FFPE tissue required 5% or more involvement.

Audit of compliance with the British Committee for Standards in Haematology (BCSH) revised guidelines for the diagnosis and assessment of treatment response of hairy cell leukemia in University Hospital Galway

INTRODUCTION

Hairy cell leukemia (HCL) is an uncommon B cell lymphoproliferative disorder. The object of the present audit was to assess whether the investigation and management of HCL in University College Hospital Galway (UCHG) complies with the British Committee for Standards in Haematology (BCSH) guidelines.

METHODS

Following a review of the records in our Haematology Department, 18 cases of HCL were identified between January 2006 and October 2014.

RESULTS

Blood film examination had been performed in all cases. Flow cytometry of liquid material had been undertaken in 89 % (n = 16) of cases, of which only 31 % (n = 5) included all four hairy cell panel markers (CD11c, CD25, CD103, CD123). Although all initial trephine biopsies included CD20, none analyzed DBA44. Only 65 % (n = 11) of treated patients had a post-treatment bone marrow biopsy preformed.

CONCLUSION

This audit highlights areas of improvement in the diagnosis and management of HCL in UCHG, which do not currently adhere to the BCSH recommendations.

BRAF inhibition in hairy cell leukemia with low-dose vemurafenib

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

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

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

Targeting Mutant BRAF in Relapsed or Refractory Hairy-Cell Leukemia

BACKGROUND

BRAF V600E is the genetic lesion underlying hairy-cell leukemia. We assessed the safety and activity of the oral BRAF inhibitor vemurafenib in patients with hairy-cell leukemia that had relapsed after treatment with a purine analogue or who had disease that was refractory to purine analogues.

METHODS

We conducted two phase 2, single-group, multicenter studies of vemurafenib (at a dose of 960 mg twice daily)--one in Italy and one in the United States. The therapy was administered for a median of 16 weeks in the Italian study and 18 weeks in the U.S. study. Primary end points were the complete response rate (in the Italian trial) and the overall response rate (in the U.S. trial). Enrollment was completed (28 patients) in the Italian trial in April 2013 and is still open (26 of 36 planned patients) in the U.S. trial.

RESULTS

The overall response rates were 96% (25 of 26 patients who could be evaluated) after a median of 8 weeks in the Italian study and 100% (24 of 24) after a median of 12 weeks in the U.S. study. The rates of complete response were 35% (9 of 26 patients) and 42% (10 of 24) in the two trials, respectively. In the Italian trial, after a median follow-up of 23 months, the median relapse-free survival was 19 months among patients with a complete response and 6 months among those with a partial response; the median treatment-free survival was 25 months and 18 months, respectively. In the U.S. trial, at 1 year, the progression-free survival rate was 73% and the overall survival rate was 91%. Drug-related adverse events were usually of grade 1 or 2, and the events most frequently leading to dose reductions were rash and arthralgia or arthritis. Secondary cutaneous tumors (treated with simple excision) developed in 7 of 50 patients. The frequent persistence of phosphorylated ERK-positive leukemic cells in bone marrow at the end of treatment suggests bypass reactivation of MEK and ERK as a resistance mechanism.

CONCLUSIONS

A short oral course of vemurafenib was highly effective in patients with relapsed or refractory hairy-cell leukemia. (Funded by the Associazione Italiana per la Ricerca sul Cancro and others; EudraCT number, 2011-005487-13; ClinicalTrials.gov number NCT01711632.).

BRAF inhibitor therapy in HCL

Targeted treatment approaches are transforming the therapeutic landscape of cancer care. The discovery of the BRAF V600E mutation in most cases of classical hairy cell leukemia opens up unique opportunities for tumor specific treatment of HCL targeting the MEK/ERK signaling pathway. The discovery and biological implications of BRAF V600E in HCL are summarized to form a basis for our current understanding of the potential for clinical exploitation. There is overwhelming clinical evidence for activity of inhibitors of BRAF in the disease. The review will review current trial activity as well as discuss novel trial concepts exploiting targeted treatment focusing on BRAF inhibition in HCL.

Long-term follow-up after purine analogue therapy in hairy cell leukaemia

Since 2006 when we last reviewed the literature concerning the use of purine analogues in hairy cell leukaemia (HCL), results from several new and updated series have been published. Here we examine these reports and consider their implications for patient management. The two purine analogues pentostatin and cladribine remain the first-line treatments of choice for all patients with HCL. Although they have not been compared in randomised trials, they appear to be equally effective. A complete response is important for the long-term outcome and we look at how best this can be achieved. Evidence is emerging which supports the use of either purine analogue plus an anti-CD20 monoclonal antibody after relapse, though questions remain concerning the scheduling of the monoclonal antibody. Patients refractory to the purine analogues may require alternative agents.

Recent advances in diagnosis and treatment of hairy cell leukemia

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

An unusual indication for splenectomy in hairy cell leukaemia: a report of three cases with persistent splenomegaly after chemoimmunotherapy

We describe three cases of relapsed hairy cell leukaemia (HCL) treated with pentostatin plus rituximab. All three achieved bone marrow complete remission but had persistent splenomegaly and hypersplenism. Because of the clinical uncertainty of its significance, they were all splenectomized. The spleen histology showed no evidence of HCL, but a five‐fold thickening of the splenic capsule and areas of fibrosis in the red pulp. This process may have contributed to the lack of elasticity and caused the persistent splenomegaly. We discuss the clinical implications for future patient management. The three patients remain in remission at 1 + , 5 +  and 9 +  years.

Current and emerging treatment options for hairy cell leukemia

Hairy cell leukemia (HCL) is a lymphoproliferative B-cell disorder characterized by pancytopenia, splenomegaly, and characteristic cytoplasmic hairy projections. Precise diagnosis is essential in order to differentiate classic forms from HCL variants, such as the HCL-variant and VH4-34 molecular variant, which are more resistant to available treatments. The current standard of care is treatment with purine analogs (PAs), such as cladribine or pentostatin, which provide a high rate of long-lasting clinical remissions. Nevertheless, ~30%–40% of the patients relapse, and moreover, some of these are difficult-to-treat refractory cases. The use of the monoclonal antibody rituximab in combination with PA appears to produce even higher responses, and it is often employed to minimize or eliminate residual disease. Currently, research in the field of HCL is focused on identifying novel therapeutic targets and potential agents that are safe and can universally cure the disease. The discovery of the BRAF mutation and progress in understanding the biology of the disease has enabled the scientific community to explore new therapeutic targets. Ongoing clinical trials are assessing various treatment strategies such as the combination of PA and anti-CD20 monoclonal antibodies, recombinant immunotoxins targeting CD22, BRAF inhibitors, and B-cell receptor signal inhibitors.