Hairy cell leukemia treated initially with purine analogs: a retrospective study of 107 patients from the Spanish Cooperative Group on Chronic Lymphocytic Leukemia (GELLC)

A 3-decade multicenter European experience with cladribine as upfront treatment in 384 hairy cell leukemia patients

Cladribine is regarded as the first treatment of choice for symptomatic hairy cell leukemia.

This large international study reports a complete response in 72% of cases and a continuous complete response in 20% of patients.

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

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

Plain Language Summary

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

Hairy Cell Leukemia Patients Have a Normal Life Expectancy-A 35-Year Single-Center Experience and Comparison with the General Population

Classic hairy cell leukemia (HCL) is an uncommon hematologic malignancy characterized by an excellent prognosis since purine analogues (PA), such as cladribine (2-CdA), have been introduced in the 1990s. However, most data on long-term outcomes is gathered from patients treated with PA first-line or include limited information on previous treatment outcomes, i.e., Interferon-α (IFN-α). Survival curves from previous series did not reach a plateau, indicating that nearly all patients ultimately relapse. Yet, overall survival (OS) data were rarely corrected for life expectancy of the general population. We here report 83 consecutive HCL patients treated between 1983 and 2017 at the University Center in Innsbruck, Austria. Median follow-up was 170 months (1-498). IFN-α, the first-line treatment of choice before 1990, was administered to 24 patients, achieving an overall response rate (ORR) of 86% and an unconfirmed complete remission (CRu) in 23%. All these patients relapsed after a median progression-free survival (PFS) of 30 months (3-80), but either remained drug-sensitive upon re-exposure to IFN-α or were successfully salvaged with PA. All 42 patients exposed to first-line 2-CdA responded (ORR of 100%). Sixteen patients received two to four successive courses of PA with a continuous decrease in the response quality (CRu rate 85.7% 1st-line vs. 41.5% 3rd-line treatment). Median PFS was not reached in both treatment-naïve patients and those retreated at first relapse. Although pretreatment with IFN-α was associated with a shortened median PFS of 81 months (43-118) after PA therapy, this tendency of inferior PFS did not result in inferior OS. OS of all 83 patients was excellent and equivalent to that of age-, sex-, and diagnostic period-matched controls from the Tyrolean general population (standardized mortality ratio 0.8), regardless of their age at diagnosis or whether they were diagnosed until or after the year 2000. These results confirm that HCL patients may look forward to a normal lifespan when treated with PA irrespective of their pretreatment history.

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.

Patients with relapsed/refractory hairy-cell leukemia

Background

Hairy cell leukemia (HCL) is a rare chronic B‐cell neoplasm with good long‐term prognosis. First and second‐line therapies include purine nucleoside analogues (PNAs) and rituximab, but until recently, limited alternative options were available for patients with two or more relapses.

Aim

The aim of this study is to describe our real‐life experience with HCL patients in third and fourth‐line therapies.

Methods and Results

Data from 49 HCL patients with two or more relapses, including 16 patients with three or more relapses, were collected from the French retrospective HCL cohort covering the period from 1980 until 2011. They were analyzed to assess hematological response, relapse free survival (RFS) and overall survival (OS) after third (L3) and fourth line (L4). The median age at diagnosis was 53 years. PNAs were the most frequently used treatments. As L3 therapy, 29 patients received PNAs (66%) and 15 (34%) other treatments (rituximab [11%] or interferon [7%] alone or in combination [16%]). The distribution of L4 treatments was similar. The overall hematological response rate (OHRR) after L3 was 97% (complete hematological response 86%) with a 40% five‐year cumulative incidence of relapse (CIR), a median RFS of 104 months, and a median OS of 235 months. After L4, the OHRR was 94% with a two‐year CIR of fourth relapse of 27%. Eleven secondary cancers (5‐year cumulative incidence of 12%) were diagnosed in 10 patients. Patients with ≥2 relapses experience frequent further relapses, with increasingly shorter time to next treatment as the number of treatment lines increases. Furthermore, treatment strategies are associated with substantial toxicities.

Conclusion

All these points lead to the need for novel treatments.

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.

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

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

[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.

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.

Hairy cell leukemia: Past, present and future

This brief review highlights the sequence of therapeutic milestones and advances in our understanding of the biology of hairy cell leukemia (HCL) with a focus on recent molecular findings and how these may be applied to improve disease outcomes in the future. Targeted therapy is discussed in the context of the recently identified BRAF mutation and other genetic findings.

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.

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.