Is there a role for minimal residual disease monitoring in the management of patients with hairy-cell leukaemia?

Long term follow-up of a phase II study of cladribine with concurrent rituximab with hairy cell leukemia variant

CDAR achieved 95% CR and 80% negative MRD, durable up to 10 years.

Carrying TP53 mutation and not achieving negative MRD after CDAR were associated with shorter survival outcomes.

Hairy cell leukemia variant (HCLv) responds poorly to purine analogue monotherapy. Rituximab concurrent with cladribine (CDAR) improves response rates, but long-term outcomes are unknown. We report final results of a phase 2 study of CDAR for patients with HCLv. Twenty patients with 0 to 1 prior courses of cladribine and/or rituximab, including 8 who were previously untreated, received cladribine 0.15 mg/kg on days 1 to 5 with 8 weekly rituximab doses of 375 mg/m² beginning day 1. Patients received a second rituximab course ≥6 months after cladribine, if and when minimal residual disease (MRD) was detected in blood. The complete remission (CR) rate from CDAR was 95% (95% confidence interval, 75-100). Sixteen (80%) of 20 patients (95% confidence interval, 56-94) became MRD negative according to bone marrow at 6 months. The median duration of MRD-negative CR was 70.1 months, and 7 of 16 are still MRD negative up to 120 months. With a median follow-up of 69.7 months, 11 patients received delayed rituximab, and the 5-year progression-free survival (PFS) and overall survival (OS) were 63.3% and 73.9%, respectively. Five patients with TP53 mutations had shorter PFS (median, 36.4 months vs unreached; P = .0024) and OS (median, 52.4 months vs unreached; P = .032). MRD-negative CR at 6 months was significantly associated with longer PFS (unreached vs 17.4 months; P < .0001) and OS (unreached vs 38.2 months; P < .0001). Lack of MRD in blood at 6 months was also predictive of longer PFS and OS (P < .0001). After progression following CDAR, median OS was 29.7 months. CDAR is effective in HCLv, with better outcomes in patients who achieve MRD-negative CR. This trial is registered at www.clinicaltrials.gov as #NCT00923013.

Droplet digital polymerase chain reaction for the assessment of disease burden in hairy cell leukemia

BRAF^V600E mutation is the pathogenic driver of hairy cell leukemia (HCL) found in the vast majority of cases both at onset and during recurrences. The identification of the mutated allele in blood and marrow correlates with the presence of neoplastic cells and can be considered a marker of active disease. Likewise, the absence of the mutation after treatment may indicate a state of deep response. The BRAF^V600E burden was measured by droplet digital polymerase chain reaction (ddPCR) and expressed as fractional abundance in 35 HCL patients at different stages of disease (onset, relapse, complete response [CR] after treatment, long-term remission) in peripheral blood and/or bone marrow (when available). Mean values of fractional abundance for patients at diagnosis, relapse and response, respectively, were 12.26%, 16.52% and 0.02% in peripheral blood and 23.51%, 13.96% and 0.26% in bone marrow. Four patients out of 6 evaluated at response were molecularly negative for BRAF^V600E in peripheral blood. Mean fractional abundance in peripheral blood tested in 14 patients with long lasting CR was 0.05%, and 10 patients were BRAF^V600E negative. These preliminary results suggest that ddPCR permits to assess the active tumor burden in HCL at different disease phases and support the hypothesis that some patients in CR qualify for a molecular CR.

[Hairy cell leukemia: What are the best treatment options for relapsed or refractory patients?]

Hairy cell leukemia is a rare form of leukemia: three hundred new cases are diagnosed each year in France. The diagnosis is based on: (1) morphological examination of the blood and bone marrow smear, (2) analysis by flow cytometry of hairy cells, which express three or the four following markers: CD11c, CD25, CD103 and CD123, (3) identification of the BRAF^V600E mutation, a true molecular marker of the disease. The management of treatment has evolved considerably in recent years. As of today, the purine analogues remain the standard treatment in the first line. Relapses are however observed in about 40% of cases. In the event of a first relapse, the preferred option is treatment with immunochemotherapy i.e. a combination of cladribine plus rituximab. Subsequent relapses are treated with moxetumomab pasudotox or BRAF inhibitors which provide indisputable benefits if third-line treatment is required. We will discuss in patients with relapsed/refractory hairy cell leukemia the needs for personalized medicine and the advantages and disadvantages of each treatment modality. The good prognosis for LT requires treatments that are not immunosuppressive, non-myelotoxic, and do not increase the risk of secondary cancers.

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.).

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 leukemia: present and future directions

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, with long-term responses to purine analogs, but with decreasing efficacy and increasing toxicity with repeated courses. Leukemic cells express CD22, CD20, CD25, tartrate-resistant acid phosphatase (TRAP), annexin 1A (Anxa1), and BRAF V600E mutation. HCLv, lacking CD25, Anxa1, TRAP, and BRAF V600E, is more aggressive and less purine analog-sensitive. A molecularly defined IGHV4-34+ variant is also resistant whether HCL or HCLv immunophenotypically. Traces of HCL cells, termed minimal residual disease (MRD), accompany most with complete remission (CR) and may cause relapse. Rituximab has limited single-agent activity, but frequent CR without MRD when combined with purine analog, albeit with chemotherapy toxicities. The anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox can achieve MRD-negative CR in multiply relapsed HCL without chemotherapy toxicities and was FDA approved in 2018 as Lumoxiti. Investigational oral non-chemotherapy options also include Vemurafenib or Dabrafenib/Trametinib targeting BRAF V600E ± MEK, and Ibrutinib targeting Bruton's tyrosine kinase.

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).