Potential predictive patterns of minimal residual disease detected by immunohistochemistry on bone marrow biopsy specimens during a long-term follow-up in patients treated with cladribine for hairy cell leukemia

Consensus opinion from an international group of experts on measurable residual disease in hairy cell leukemia

A significant body of literature has been generated related to the detection of measurable residual disease (MRD) at the time of achieving complete remission (CR) in patients with hairy cell leukemia (HCL). However, due to the indolent nature of the disease as well as reports suggesting long-term survival in patients treated with a single course of a nucleoside analog albeit without evidence of cure, the merits of detection of MRD and attempts to eradicate it have been debated. Studies utilizing novel strategies in the relapse setting have demonstrated the utility of achieving CR with undetectable MRD (uMRD) in prolonging the duration of remission. Several assays including immunohistochemical analysis of bone marrow specimens, multi-parameter flow cytometry and molecular assays to detect the mutant BRAF V600E gene or the consensus primer for the immunoglobulin heavy chain gene (IGH) rearrangement have been utilized with few comparative studies. Here we provide a consensus report on the available data, the potential merits of MRD assessment in the front-line and relapse settings and recommendations on future role of MRD assessment in HCL.

Measurable residual disease in hairy cell leukemia: Technical considerations and clinical significance

Hairy cell leukemia (HCL) is a rare type of chronic lymphoid leukemia originating from a mature B lymphocyte. A diagnosis of HCL is based on cytology, confirmed by multiparametric flow cytometry (MFC) studies using anti-B-cell monoclonal antibodies, together with a panel of antibodies more specific to HCL, such as CD11c, CD25, CD103 and CD123. Recently, the BRAF V600E mutation has been described as a disease-defining genetic event. Measurable residual disease (MRD) is defined as the lowest level of HCL cells that can be detected accurately and reproducibly using validated methods; as MRD negativity is associated with high rates of durable complete response, by clearing MRD, the long-term outcome may be improved in patients with advanced HCL. MRD is typically detected using bone marrow, and in some cases, peripheral blood; however, in HCL, discrepancies frequently exist between MRD results obtained from blood, bone marrow aspirate and core biopsy. Among the methods used for MRD detection, MFC appears to be a more sensitive technique than immunohistochemistry. Molecular tests are also used, such as real-time quantitative PCR for unique immunoglobulin heavy chain (IgH) gene rearrangements and PCR techniques with clone specificity for BRAF V600E. Clone-specific PCR (spPCR) is able to detect one HCL cell in 106 normal cells, and is particularly suitable for patients found to be negative for MRD by MFC. Recently, the Hairy Cell Leukemia Consortium created a platform to work on a definition for MRD, and establish the optimal time point, tissue type and method for measuring MRD. This

Moxetumomab Pasudotox in Hairy Cell Leukaemia: A Profile of Its Use

Moxetumomab pasudotox (Lumoxiti^®), an anti-CD22 recombinant immunotoxin, is an important treatment option that is approved in adults with relapsed or refractory hairy cell leukaemia (HCL) who have received at least two prior lines of treatment with systemic therapies including purine nucleoside analogues. In a pivotal phase III trial, treatment with moxetumomab pasudotox resulted in approximately one third of patients achieving durable complete response lasting more than 6 months, as well as improvements in other haematological parameters and disease-related symptoms. Moxetumomab pasudotox had a generally manageable tolerability profile; the most common treatment-related adverse events (AEs) included nausea, peripheral oedema, headache and pyrexia. AEs of special interest (including haemolytic uraemic syndrome and capillary leak syndrome) were generally manageable and reversible with monitoring and supportive care.

Management of Relapsed Hairy Cell Leukemia: A Systematic Review of Novel Agents and Targeted Therapies

BACKGROUND

Hairy cell leukemia (HCL) responds well to purine analogs with an overall median relapse free survival of 11-16 years. Most patients can be retreated with the same or a different purine analog however a subset of patients will become resistant or develop cumulative toxicities. Novel agents such as Vemurafenib (BRAF kinase inhibitor), Bendamustine/Rituximab (BR), Moxetumomab pasudotox (anti CD-22 recombinant immunotoxin) and Ibrutinib have emerging roles in patients with relapsed HCL.

METHODS

Five databases (PubMed, Embase, Cochrane Library, Web of Science and ClinicalTrials.gov) were searched using the following search terms: "hairy cell leukemia" or "leukemia, hairy cell" AND "relapse" or "recurrence". We included only prospective clinical trials with outcome data.

RESULTS

Vemurafenib monotherapy was evaluated in two separate arms of a phase 2 trial. In the US arm (n=24), the ORR was 100% (CR 42%; PR 58%). In the Italian arm (n=26), the ORR was 96% (CR 35%; PR 62%). In a phase 2 study (n=25), the combination of vemurafenib and rituximab showed CR of 100%. The combination of BR achieved an ORR of 100% whereas CR was 50% and 67% at a bendamustine dose of 70mg/m² (n=6) and 90 mg/m² (n=6) respectively. In a phase 3 trial, moxetumomab pasudotox (n=80) had an ORR of 75% (CR 41%). Single agent Ibrutinib (n=37) had an ORR of 54%. Therapies were generally well tolerated.

CONCLUSION

Novel agents have good efficacy in HCL in patients with multiple relapses.

Prospective long-term follow-up after first-line subcutaneous cladribine in hairy cell leukemia: a SAKK trial

Hairy cell leukemia (HCL) remains an incurable disease. However, first-line treatment with either intravenous or subcutaneous cladribine generally leads to long-lasting remissions. Although there are excellent long-term data for intravenous application, similar data regarding subcutaneous administration are lacking. We therefore analyzed the long-term outcome of 3 prospective multicenter clinical trials on subcutaneous cladribine performed by the Swiss Group for Clinical Cancer Research (SAKK), which recruited 221 patients with classical HCL between 1993 and 2005. Median overall survival from start of treatment was not reached. Pretreatment anemia, higher Eastern Cooperative Oncology Group score, and higher age were associated with poorer overall survival in multivariable analysis, whereas early progression at 24 and 36 months had no significant impact on overall survival. Second-line treatment was necessary in 53 (23.7%) patients after a median of 5 (range, 0.2-20.4) years, and first retreatment was mainly monotherapy with cladribine (66%) or rituximab (15.1%) or a combination of these drugs (15.1%). A total of 44 (19.9%) patients developed second primary malignancies with a median time to occurrence of 5.7 (range, 0.01-17.5) years. Second primary malignancies were the main cause for death (14; 27.5%). Compared with a matched normal Swiss population, the incidence of second primary malignancies was not increased. However, survival of patients with HCL was slightly inferior by comparison (P = .036). In conclusion, the outcome of HCL patients treated with subcutaneous cladribine is excellent, and in most patients, 1 cycle of subcutaneous cladribine is sufficient for long-term disease control.

Moxetumomab pasudotox in heavily pre-treated patients with relapsed/refractory hairy cell leukemia (HCL): long-term follow-up from the pivotal trial

Background

Moxetumomab pasudotox is a recombinant CD22-targeting immunotoxin. Here, we present the long-term follow-up analysis of the pivotal, multicenter, open-label trial (NCT01829711) of moxetumomab pasudotox in patients with relapsed/refractory (R/R) hairy cell leukemia (HCL).

Methods

Eligible patients had received ≥ 2 prior systemic therapies, including ≥ 2 purine nucleoside analogs (PNAs), or ≥ 1 PNA followed by rituximab or a BRAF inhibitor. Patients received 40 µg/kg moxetumomab pasudotox intravenously on Days 1, 3, and 5 of each 28-day cycle for up to six cycles. Disease response and minimal residual disease (MRD) status were determined by blinded independent central review. The primary endpoint was durable complete response (CR), defined as achieving CR with hematologic remission (HR, blood counts for CR) lasting > 180 days.

Results

Eighty adult patients were treated with moxetumomab pasudotox and 63% completed six cycles. Patients had received a median of three lines of prior systemic therapy; 49% were PNA-refractory, and 38% were unfit for PNA retreatment. At a median follow-up of 24.6 months, the durable CR rate (CR with HR > 180 days) was 36% (29 patients; 95% confidence interval: 26–48%); CR with HR ≥ 360 days was 33%, and overall CR was 41%. Twenty-seven complete responders (82%) were MRD-negative (34% of all patients). CR lasting ≥ 60 months was 61%, and the median progression-free survival without the loss of HR was 71.7 months. Hemolytic uremic and capillary leak syndromes were each reported in ≤ 10% of patients, and ≤ 5% had grade 3–4 events; these events were generally reversible. No treatment-related deaths were reported.

Conclusions

Moxetumomab pasudotox resulted in a high rate of durable responses and MRD negativity in heavily pre-treated patients with HCL, with a manageable safety profile. Thus, it represents a new and viable treatment option for patients with R/R HCL, who currently lack adequate therapy.

Trial registration

ClinicalTrials.gov identifier: NCT01829711; first submitted: April 9, 2013. https://clinicaltrials.gov/ct2/show/NCT01829711

Supplementary information

Supplementary information accompanies this paper at 10.1186/s13045-020-01004-y.

Hairy Cell Leukaemia

PURPOSE OF REVIEW

To summarise diagnostic clinical/laboratory findings and highlight differences between classical hairy cell leukaemia (HCLc) and hairy cell leukaemia variant (HCLv). Discussion of prognosis and current treatment indications including novel therapies, linked to understanding of the underlying molecular pathogenesis.

RECENT FINDINGS

Improved understanding of the underlying pathogenesis of HCLc, particularly the causative mutation BRAF V600E, leading to constitutive activation of the MEK/ERK signalling pathway and increased cell proliferation. HCLc is caused by BRAF V600E mutation in most cases. Purine nucleoside analogue (PNA) therapy is the mainstay of treatment, with the addition of rituximab, improving response and minimal residual disease (MRD) clearance. Despite excellent responses to PNAs, many patients will eventually relapse, requiring further therapy. Rarely, patients are refractory to PNA therapy. In relapsed/refractory patients, novel targeted therapies include BRAF inhibitors (BRAFi), anti-CD22 immunoconjugate moxetumomab and Bruton tyrosine kinase inhibitors (BTKi). HCLv has a worse prognosis with median overall survival (OS), only 7-9 years, despite the combination of PNA/rituximab improving front-line response. Moxetumomab or ibrutinib may be a viable treatment but lacks substantial evidence.

Moxetumomab pasudotox for the treatment of relapsed and/or refractory hairy cell leukemia

Introduction: Hairy cell leukemia is a rare indolent B-cell malignancy, characterized by pancytopenia, recurrent infections, and splenomegaly. After initial therapy with purine nucleoside analogs, up to 50% of patients relapse after several years of remission. The number of relapsed patients is increasing and, until recently, there was no approved therapy with durable responses for hairy cell leukemia patients in the relapsed setting, thus the need for new non-chemotherapy approach with significant efficacy and less myelosuppression. Areas covered: Moxetumomab pasudotox is a recombinant immunotoxin containing a Fv fragment of an anti-CD22 monoclonal antibody and truncated Pseudomonas exotoxin (PE38). The authors reviewed pre-clinical and clinical studies that led to the FDA approval of the drug in patients with relapsed and/or refractory hairy cell leukemia, who received at least two prior therapies, including at least one purine nucleoside analog. Expert opinion: Moxetumomab pasudotox demonstrated a durable complete remission rate of 30% in heavily pretreated patients with hairy cell leukemia, and MRD eradication in 85% of responding patients. Moxetumomab pasudotox got a global FDA approval in September 2018. The US prescribing information carries boxed warnings regarding the risk of capillary leak syndrome and hemolytic uremic syndrome. Long-term follow-up of the pivotal study is ongoing (NCT01829711).

Moxetumomab pasudotox-tdfk for relapsed/refractory hairy cell leukemia: a review of clinical considerations

PURPOSE

Hairy cell leukemia (HCL) is a rare mature B cell leukemia. Purine analogs are the mainstay of treatment of HCL, but relapse after purine analog therapy is common. Outcomes of treatment of relapsed/refractory HCL typically diminish with each successive line of therapy. Moxetumomab pasudotox-tdfk is a novel recombinant immunotoxin approved for the treatment of patients with relapsed/refractory HCL who have received at least two prior therapies, including a purine analog. This article reviews HCL treatment, focusing on moxetumomab pasudotox-tdfk, its place in therapy, considerations for preparation and administration, and strategies for prevention and management of toxicities.

METHODS

A literature search was conducted in the PubMed database from inception to January 2019, using the following terms: moxetumomab, hairy cell leukemia, relapsed/refractory hairy cell leukemia, immunotoxin, and CD22. The package insert and available posters and abstracts were also reviewed.

RESULTS

FDA approval of moxetumomab pasudotox-tdfk was based on a phase III single-arm, open-label trial in 80 patients. Treatment with moxetumomab pasudotox-tdfk yielded a durable complete response rate of 30% with a median duration of response that had not yet been reached at a median follow-up of 16.7 months. The objective response rate was 75% based on blinded independent central review. The most common adverse reactions were infusion-related reactions, edema, nausea, fatigue, headache, pyrexia and anemia. Serious adverse events include capillary leak syndrome and hemolytic uremic syndrome.

CONCLUSIONS

Clinicians providing care for patients receiving moxetumomab pasudotox-tdfk should be aware of the strategies required for safe administration, including the management of serious adverse events.

Phase 1 study of PSMA ADC, an antibody-drug conjugate targeting prostate-specific membrane antigen, in chemotherapy-refractory prostate cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a well-characterized target that is overexpressed selectively on prostate cancer cells. PSMA antibody-drug conjugate (ADC) is a fully human IgG1 monoclonal antibody conjugated to the microtubule disrupting agent monomethyl auristatin E (MMAE), which is designed to specifically bind PSMA-positive cells, internalize, and then release its cytotoxic payload into the cells. PSMA ADC has demonstrated potent and selective antitumor activity in preclinical models of advanced prostate cancer. A Phase 1 study was conducted to assess the safety, pharmacokinetics, and preliminary antitumor effects of PSMA ADC in subjects with treatment-refractory prostate cancer.

METHODS

In this first-in-man dose-escalation study, PSMA ADC was administered by intravenous infusion every three weeks to subjects with progressive metastatic castration-resistant prostate cancer (mCRPC) who were previously treated with docetaxel chemotherapy. The primary endpoint was to establish a maximum tolerated dose (MTD). The study also examined the pharmacokinetics of the study drug, total antibody, and free MMAE. Antitumor effects were assessed by measuring changes in serum prostate-specific antigen (PSA), circulating tumor cells (CTCs), and radiologic imaging.

RESULTS

Fifty-two subjects were administered doses ranging from 0.4 to 2.8 mg/kg. Subjects had a median of two prior chemotherapy regimens and prior treatment with abiraterone and/or enzalutamide. Neutropenia and peripheral neuropathy were identified as important first-cycle and late dose-limiting toxicities, respectively. The dose of 2.5 mg/kg was determined to be the MTD. Pharmacokinetics were approximately dose-proportional with minimal drug accumulation. Reductions in PSA and CTCs in subjects treated with doses of ≥1.8 mg/kg were durable and often concurrent.

CONCLUSIONS

In an extensively pretreated mCRPC population, PSMA ADC demonstrated acceptable toxicity. Antitumor activity was observed over dose ranges up to and including 2.5 mg/kg. The observed anti-tumor activity supported further evaluation of this novel agent for the treatment of advanced metastatic prostate cancer.

Moxetumomab pasudotox: A first-in-class treatment for hairy cell leukemia

Hairy cell leukemia is a rare indolent B-cell lymphoid malignancy. Durable remission can be obtained with purine analogues, but relapse is inevitable, and effective treatment options may be limited. Moxetumomab pasudotox is a recombinant CD22-targeting immunotoxin that has recently been approved by the United States Food and Drug Administration for the treatment of relapsed or refractory hairy cell leukemia. Approval was based on a pivotal phase III study in this unique patient population. Rationale for use, clinical trial data, and current treatment recommendations are detailed. Common adverse effects are reviewed, and management strategies for select adverse effects are suggested. Implications for contemporary practitioners are also provided, as use of this novel agent is likely to increase as follow-up studies are reported.

Moxetumomab pasudotox in relapsed/refractory hairy cell leukemia

This is a pivotal, multicenter, open-label study of moxetumomab pasudotox, a recombinant CD22-targeting immunotoxin, in hairy cell leukemia (HCL), a rare B cell malignancy with high CD22 expression. The study enrolled patients with relapsed/refractory HCL who had ≥2 prior systemic therapies, including ≥1 purine nucleoside analog. Patients received moxetumomab pasudotox 40 µg/kg intravenously on days 1, 3, and 5 every 28 days for ≤6 cycles. Blinded independent central review determined disease response and minimal residual disease (MRD) status. Among 80 patients (79% males; median age, 60.0 years), durable complete response (CR) rate was 30%, CR rate was 41%, and objective response rate (CR and partial response) was 75%; 64 patients (80%) achieved hematologic remission. Among complete responders, 27 (85%) achieved MRD negativity by immunohistochemistry. The most frequent adverse events (AEs) were peripheral edema (39%), nausea (35%), fatigue (34%), and headache (33%). Treatment-related serious AEs of hemolytic uremic syndrome (7.5%) and capillary leak syndrome (5%) were reversible and generally manageable with supportive care and treatment discontinuation (6 patients; 7.5%). Moxetumomab pasudotox treatment achieved a high rate of independently assessed durable response and MRD eradication in heavily pretreated patients with HCL, with acceptable tolerability.

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.

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.

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.

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.

Novel therapeutic options for relapsed hairy cell leukemia

The majority of patients with hairy cell leukemia (HCL) achieve a response to therapy with cladribine or pentostatin with or without rituximab. However, late relapses can occur. Treatment of relapsed HCL can be difficult due to a poor tolerance to chemotherapy, increased risk of infections and decreased responsiveness to chemotherapy. The identification of BRAFV600E mutations and the role of aberrant MEK kinase and Bruton's tyrosine kinase (BTK) pathways in the pathogenesis of HCL have helped to develop novel targeted therapies for these patients. Currently, the most promising therapeutic strategies for relapsed or refractory HCL include recombinant immunoconjugates targeting CD22 (e.g. moxetumomab pasudotox), BRAF inhibitors such as vemurafenib and B cell receptor signaling kinase inhibitors such as ibrutinib. Furthermore, the VH4-34 molecular variant of classic HCL has been identified to be less responsive to chemotherapy. Herein, we review the results of the ongoing clinical trials and potential future therapies for relapsed/refractory HCL.

Hairy cell leukemia: Update on molecular profiling and therapeutic advances

Hairy cell leukemia was initially described as a clinicopathologic entity more than 50 years ago. We have subsequently discovered that HCL is really at least two diseases: classical HCL and the hairy cell leukemia variant. The former is among a small group of cancers exceptional for being (nearly) unified by a single genetic lesion, the BRAF V600E mutation. Over the past three decades, tremendous progress in both diagnostic and prognostic clarification has been accompanied by therapeutic advances in classical HCL. Consequently, this once uniformly fatal disease has been converted in most cases into a chronic illness enabling patients to live long and productive lives. In response to standard therapy, patients have high complete remission rates. Unfortunately, the long-term survival curves have not plateaued, revealing that this disease is controlled but not cured. Though rare and representing only about 10% of an already rare disease, those patients with the variant fare exceptionally poorly with standard therapy: complete response rates to purine nucleoside analogs are reported to be less than 50%, whereas the complete response rates in classical HCL are up to 90%. Novel small molecules targeting BRAF and the B-cell receptor signaling complex, and biologic agents like antibodies and immunotoxin conjugates are being explored for those patients who have relapsed. Substantial opportunities for continued research remain. This complex and multi-faceted disease incorporates challenges from altered immunity associated with the underlying disease and its treatments. Considering the rarity of this malignancy, optimization of patient management requires multi-institutional collaboration. The Hairy Cell Leukemia Foundation (www.hairycellleukemia.org) was formed to coordinate these efforts.

Update on the biology and treatment options for hairy cell leukemia

Hairy cell leukemia (HCL) is an uncommon chronic leukemia of mature B cells. Leukemic B cells of HCL exhibit a characteristic morphology and immunophenotype and coexpress multiple clonally related immunoglobulin isotypes. Precise diagnosis and detailed workup is essential, because the clinical profile of HCL can closely mimic that of other chronic B-cell lymphoproliferative disorders that are treated differently. Variants of HCL, such as HCLv and VH4-34 molecular variant, vary in the immunophenotype and specific VH gene usage, and have been more resistant to available treatments. On the contrary, classic HCL is a highly curable disease. Most patients show an excellent long-term response to treatment with single-agent cladribine or pentostatin, with or without the addition of an anti-CD20 monoclonal antibody such as rituximab. However, approximately 30-40 % of patients with HCL relapse after therapy; this can be treated with the same purine analogue that was used for the initial treatment. Advanced molecular techniques have identified distinct molecular aberrations in the Raf/MEK-ERK pathway and BRAF (V600E) mutations that drive the proliferation and survival of HCL B cells. 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. Ongoing and planned clinical trials are assessing various treatment strategies, such as the combination of purine analogues and various anti-CD20 monoclonal antibodies, recombinant immunotoxins targeting CD22 (e.g., moxetumomab pasudotox), BRAF inhibitors, such as vemurafenib, and B-cell receptor signaling inhibitors, such as ibrutinib, which is a Bruton's tyrosine kinase inhibitor. This article provides an update of our current understanding of the pathophysiology of HCL and the treatment options available for patients with classic HCL. Discussion of variant forms of HCL is beyond the scope of this manuscript.

Cladribine with immediate rituximab for the treatment of patients with variant hairy cell leukemia

PURPOSE

In contrast with the classic form, variant hairy cell leukemia (HCLv) responds poorly to single-agent purine analogs, expresses unmutated BRAF, has shorter overall survival, and lacks effective standard therapy. No treatment has achieved a high complete remission (CR) rate even in small series, and of 39 reported cases from six studies, overall response rate after cladribine was 44% with 8% CRs. Rituximab has been found to increase the sensitivity of malignant cells to cladribine, suggesting that combination with cladribine might improve response in HCLv. To test this hypothesis, patients with HCLv were treated with simultaneous cladribine and rituximab.

EXPERIMENTAL DESIGN

Patients with HCLv with 0 to 1 prior courses of cladribine received cladribine 0.15 mg/kg for days 1 to 5, with eight weekly doses of rituximab 375 mg/m(2) beginning day 1. Restaging was performed, and minimal residual disease (MRD) in blood and marrow was quantified using PCR, immunohistochemistry, and flow cytometry.

RESULTS

By 6 months, 9 (90%) of 10 patients achieved CR, compared with 3 (8%) of 39 reported cases treated with cladribine alone (P < 0.0001). Of the 9 CRs, 8 remain free of MRD at 12 to 48 (median 27) months of follow-up. No dose-limiting toxicities were observed when beginning cladribine and rituximab on the same day, although most patients required short-term steroids to prevent and treat rituximab infusion reactions. Cytopenias in CRs resolved in 7 to 211 (median 34) days without major infections.

CONCLUSION

Although cladribine alone lacks effectiveness for early or relapsed HCLv, cladribine with immediate rituximab achieves CRs without MRD and is feasible to administer.

Revised guidelines for the diagnosis and management of hairy cell leukaemia and hairy cell leukaemia variant*

The British Committee for Standards in Haematology first produced guidelines for the diagnosis and management of hairy cell leukaemia and hairy cell leukaemia variant in 2000. This revision updates those guidelines and covers the areas of diagnosis, treatment and assessment of response to therapy.

Implications of minimal residual disease in hairy cell leukemia after cladribine using immunohistochemistry and immunophenotyping

Hairy cell leukemia (HCL) is a highly treatable, but generally incurable B-cell lymphoproliferative disorder with a long natural history. The purine analogs cladribine and pentostatin are the treatments of choice and both induce complete remission (CR) by peripheral blood counts and morphologic examination of the marrow in the large majority of patients. However, some patients, otherwise in apparent CR, have evidence of minimal residual disease (MRD) as detected by a number of different techniques, including immunohistochemistry, immunophenotypying by flow cytometry, and polymerase chain reaction (PCR). Immunohistochemistry is readily available, but precise criteria which constitute MRD are not uniform. Immunophenotyping can identify a characteristic immunophenotype, but leukemia cells may be difficult to obtain from a fibrotic bone marrow. Patient-specific PCR, while highly specific, is not readily available. Furthermore, the introduction of newer effective therapies such as the monoclonal antibody rituximab and immunoconjugate BL22 following a purine analog or concurrently with a purine analog may eradicate MRD. However, the optimal method for detecting MRD is not known. Furthermore, whether the eradication of MRD improves overall survival has not been established.

Definition of remission, minimal residual disease, and relapse in hairy cell leukemia bone marrow biopsy histology and immunohistology specimens

No consensus has been reached in the definitions of complete remission (CR) and minimal residual disease (MRD) on bone marrow biopsy specimens of patients with hairy cell leukemia (HCL). Large comparative studies correlating clinical outcome with detection of MRD by immunohistochemistry (IHC), flow cytometry, and molecular diagnostics are lacking. The presence of normal bone marrow B-lymphocytes and the lack of immunohistochemical stains that are both sensitive and specific can make it challenging to differentiate normal lymphocytes from hairy cells. The use of CD20 and/or DBA.44 immunohistochemical stains, in combination with either tartrate resistant acid phosphatase (TRAP), CD11c-5D11, or annexin A1, improve specificity and facilitate evaluation. The interobserver concordance in quantifying the percentage of residual hairy cells is poor. Performing cell counts in multiple fields improves reproducibility. The prolonged hematologic remissions of subsets of patients with MRD emphasize the need to define clinically relevant thresholds that correlate with long-term responses and clinical endpoints. The development of internationally accepted, reproducible, and clinically relevant CR, MRD, and relapse criteria are of paramount importance in evaluating and comparing clinical trials and in providing optimal patient care.

Sustained long-term remissions with weekly interferon maintenance therapy in hairy cell leukemia

AIM

This study evaluates the efficacy of weekly α-interferon (IFN) maintenance therapy in hairy cell leukaemia (HCL), a disease that remains incurable.

METHOD

Nine patients (six male, three female, aged 41-69 yrs) with hairy cell leukaemia (HCL) received IFN 3mU s.c. once weekly as long-term maintenance therapy after achieving optimal clinical and hematological response to initial therapy with thrice weekly IFN.

RESULTS

Eight of the nine patients are in a state of sustained response at 3-17 years (median 12 years).

CONCLUSION

Our results are similar to those from three previous studies using long-term IFN maintenance therapy, bringing the total number of patients in sustained remission to 118. We hope these reports will lead to a multi-centre, phase III study of IFN maintenance therapy (including pegylated IFN, given less frequently) in HCL patients achieving optimal response to initial therapy, be it IFN or a purine analogue.

How I treat hairy cell leukemia

The description of hairy cell leukemia as a specific clinical entity was published 50 years ago. The clinical outcome for patients was hampered by ineffective chemotherapy, and splenectomy was the major therapeutic approach to improve peripheral blood counts. The median survival after diagnosis was 4 years. With the introduction of alpha-interferon in 1984, marked improvements in patient responses were observed. Shortly thereafter, the introduction of the purine nucleoside analogs transformed this disease into a highly treatable form of leukemia, and patients with the classic form of this rare leukemia now have a near-normal life expectancy. However, other clinical entities mimicking this disease do not respond; thus, accurate diagnosis is important. Immunophenotypic features in classic hairy cell leukemia show that the leukemic cells express CD11c, CD25, CD103, and CD123 and display bright CD20. Despite the high percentage of durable complete remissions with modern therapy, the long-term disease-free survival curves have not reached a plateau. Many patients who achieve a complete remission by morphologic criteria have minimal residual disease demonstrable by either flow cytometry or immunohistochemical staining, and this population may be at higher risk for earlier relapse. Continued clinical research is essential to optimize therapy for this disease.

2-CdA in the treatment of hairy cell leukemia: a review of long-term follow-up

Hairy cell leukemia is a rare, indolent, chronic lymphoproliferative disorder characterized by the proliferation of a malignant B-cell clone with irregular cytoplasmic projections. Treatment with purine analogs such as 2-chlorodeoxyadenosine (2-CdA) is associated with excellent remission rates and long-term survival. Although the majority of patients achieve a complete remission (CR), most have minimal residual disease detected by sensitive methods. Despite the long term disease-free survival, approximately 36% of patients relapse and many require further therapy. Repeat administration of 2-CdA is very effective in achieving a second CR. Recently, new agents such rituximab and BL22 were shown to be effective in the treatment of relapsed and refractory disease.

The role of rituximab in combination with pentostatin or cladribine for the treatment of recurrent/refractory hairy cell leukemia

BACKGROUND

The purine analogs pentostatin and cladribine have revolutionized the treatment of hairy cell leukemia (HCL) with overall responses in greater than 85% of patients and a median progression-free survival of up to 15 years. They continue to be effective at second- and even third-line therapy; however, alternative treatments are needed for patients who are or have become refractory to these agents or whose remissions are shorter with each course of therapy.

METHODS

The authors conducted a retrospective review of 8 patients who received pentostatin or cladribine combined concurrently (n = 6 patients) or sequentially (n = 2 patients) with rituximab at second-line therapy (n = 3 patients) and at subsequent lines of therapy (n = 5 patients). Results from a previously reported database of 219 patients with HCL (73 patients who received second-line therapy and 20 patients who received third-line therapy) were used as a historic control group against which to measure benefit.

RESULTS

All 8 patients responded to therapy, with 7 complete responses (CRs) (87.5%) and minimal toxicity. All patients who had CRs were negative for minimal residual disease (MRD). At a median follow-up of 29 months (range, 5-39 months) 1 patient developed recurrent disease, and the estimated 2-year recurrence rate was 20% (0% after second-line therapy and 25% after subsequent lines of therapy). In the historic control group, the CR rates were 70% after second-line therapy and 45% after third-line therapy, and the recurrence rates at 2 years were 15% and 33%, respectively.

CONCLUSIONS

The combination of purine analogs with rituximab was safe and effective for patients with recurrent and/or refractory HCL, and the current results suggested an added benefit compared with standard treatment.

Pentostatin: impact on outcome in hairy cell leukemia

Major advances in the management of patients who have hairy cell leukemia have been made following the use of purine nucleoside analogs. Pentostatin and cladribine are equally effective, and have impressive long-term effectiveness. Although the degree of myelosuppression may be less with the use of pentostatin, this may reflect differences in the schedule and dose of drug administration between these agents. The gradual, but relentless, improvement in the peripheral blood counts enables out-patient management with pentostatin in most patients. Cladribine affords the convenience of a single course of administration. A direct comparative study with these two agents is unlikely to yield the optimal management of patients who have minimal residual disease following the administration of either agent is warranted in the context of a clinical trial. Patients do relapse, and the overall survival curves have not reached a plateau, which indicates that cure has not been secured. The satisfaction of having improved the outcome for patients who have this previously untreatable leukemia should not give way to complacency for further improvement in the management of this disease. Future studies should be directed to optimizing the therapy for minimal residual disease as well as clearer definition of supportive care.

Hairy cell leukemia

Hairy cell leukemia is a rare B-cell neoplasm. When treated with either pentostatin or cladribine, complete and durable remissions can be secured and life expectancy for most patients is normal. A small minority of patients require alternative treatment with monoclonal antibodies or immunotoxins. Patients who attain a complete response to first-line treatment have the best prognosis.

Current treatment options in hairy cell leukemia and hairy cell leukemia variant

Hairy cell leukemia (HCL) is a chronic B-cell lymphoproliferative disorder characterized by splenomegaly, pancytopenia and circulating lymphocytes displaying prominent cytoplasmic projections. HCL has usually an indolent course and the patients with asymptomatic disease do not require therapy. Treatment of progressive symptomatic HCL includes a variety of pharmacological approaches such as interferon-alpha (IFN-alpha), pentostatin (DCF) and cladribine (2-CdA), which have significantly improved the disease prognosis. 2-CdA and DCF seem to induce a similar high response rate and a long overall survival. They are also active in relapsed patients. More recently high activity of anti-CD20 monoclonal antibody (rituximab) and anti-CD25 (LMB-2) and anti-CD22 (BL-22) immunotoxins have increased the number of therapeutic options for HCL. Splenectomy may be still indicated in patients with massive, symptomatic splenomegaly or results in severe cytopenia. IFN-alpha may have a place in patients with very severe cytopenia, in HCL in pregnancy and in patients who have failed prior therapy with purine nucleoside analogs. HCL variant (HCL-V) is a distinct clinico-pathological entity which seems to be resistant to IFN-alpha and purine nucleoside analogs - DCF and 2-CdA. However, preliminary observations suggest that monoclonal antibodies - rituximab and BL-22 immunotoxin are highly active in this disorder even refractory to 2-CdA. In this review current therapeutic strategies in HCL and HCL-V are presented.