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

Diagnosis and treatment of hairy cell leukemia as the COVID-19 pandemic continues

Hairy cell leukemia (HCL) is an indolent B-cell malignancy, usually driven by the BRAF V600E mutation. For 30 years, untreated and relapsed HCL was successfully treated with purine analogs, but minimal residual disease (MRD) remained in most patients, eventually causing relapse. Repeated purine analogs achieve decreasing efficacy and increasing toxicity, particularly to normal T-cells. MRD-free complete remissions (CRs) are more common using rituximab with purine analogs in both 1^st-line and relapsed settings. BRAF inhibitors and Ibrutinib can achieve remission, but due to persistence of MRD, must be used chronically to prevent relapse. BRAF inhibition combined with Rituximab can achieve high MRD-free CR rates. Anti-CD22 recombinant immunotoxin moxetumomab pasudotox is FDA-approved in the relapsed setting and is unique in achieving high MRD-free CR rates as a single-agent. Avoiding chemotherapy and rituximab may be important in ensuring both recovery from COVID-19 and successful COVID-19 vaccination, an area of continued investigation.

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.).

Treatment of hairy cell leukemia

INTRODUCTION

Purine analogs made dramatic improvements for patients with hairy cell leukemia (HCL), but patients often relapse, require multiple treatments, and may become refractory. Major developments in treatment of relapsed/refractory HCL occurred with discovery of disease biology. New agents increase the complexity of clinical decision-making.

AREAS COVERED

Anti-CD22 recombinant immunotoxin Moxetumomab Pasudotox (Moxe), CD20 Mabs rituximab and obinutuzumab, BRAF/MEK inhibitors vemurafenib and dabrafenib-trametinib, and Bruton's tyrosine kinase (BTK) inhibitor ibrutinib have been tested in HCL. All show efficacy but with different treatment durations and response rates, including for eradicating minimal residual disease (MRD). Side effects differ and must be considered when selecting treatment. Studies from PubMed indexed papers and abstracts presented at major international conferences are included.

EXPERT OPINION

Rituximab with either purine analog or BRAF-inhibitor achieves high rates of MRD-free complete remission (CR). Moxe achieves MRD-free CR without chemotherapy toxicities. Moxe should be considered prior to splenectomy or development of adenopathy. BRAF/MEK inhibition and ibrutinib are effective options but most patients remain MRD+, requiring indefinite treatment or rituximab to prevent relapse. Under investigation is MRD elimination with CD20 antibody combined with Moxe or BRAF inhibitor. High-risk diseases including HCL variant and IGHV4-34+ unmutated HCL require further investigation.

Development of Recombinant Immunotoxins for Hairy Cell Leukemia

Hairy cell leukemia (HCL) is an indolent B-cell malignancy with excellent initial response to purine analogs pentostatin or cladribine, but patients are rarely, if ever, cured. Younger patients will usually need repeat chemotherapy which has declining benefits and increasing toxicities with each course. Targeted therapies directed to the BRAF V600E mutation and Bruton's tyrosine kinase may be helpful, but rarely eradicate the minimal residual disease (MRD) which will eventually lead to relapse. Moxetumomab pasudotox (Moxe) is an anti-CD22 recombinant immunotoxin, which binds to CD22 on HCL cells and leads to apoptotic cell death after internalization and trafficking of the toxin to the cytosol. Phase I testing achieved a complete remission (CR) rate of 57% in relapsed/refractory HCL. Most CRs were without MRD and eradication of MRD correlated with prolonged CR duration. Patients were often MRD-free after five years. Important mild-moderate toxicities included capillary leak and hemolytic uremic syndromes which could be prevented and managed conservatively. A phase 3 trial met its endpoint of durable CR with acceptable toxicity, leading to FDA approval of Moxe for relapsed/refractory HCL, under the name Lumoxiti. Moxe combined with rituximab is currently being evaluated in relapsed/refractory HCL to improve the rate of MRD-free CR.

Randomized Phase II Study of First-Line Cladribine With Concurrent or Delayed Rituximab in Patients With Hairy Cell Leukemia

PURPOSE

Single-agent purine analog, usually cladribine, has been the standard first-line therapy of hairy cell leukemia (HCL) for 30 years. High complete remission (CR) rates often include minimal residual disease (MRD), leading to relapse and repeated treatments. Rituximab can clear MRD, but long-term results are unknown and optimal timing of rituximab undefined.

PATIENTS AND METHODS

Patients were randomly assigned to first-line cladribine 0.15 mg/kg intravenously days 1-5 with 8 weekly doses of rituximab 375 mg/m² begun either day 1 (concurrent, CDAR) or ≥ 6 months later (delayed) after detection of MRD in blood. MRD tests included blood and bone marrow (BM) flow cytometry, and BM immunohistochemistry.

RESULTS

Sixty-eight patients with purine analog-naïve classic HCL were randomly assigned 1:1 to concurrent versus delayed arms. At 6 months after CDAR versus cladribine monotherapy, CR rates were 100% versus 88% (P = .11), MRD-free CR rates 97% versus 24% (P < .0001, primary end point), and blood MRD-free rates 100% versus 50% (P < .0001), respectively. At 96 months median follow-up, 94% versus 12% remained MRD free. Compared with CDAR, delayed rituximab after cladribine achieved lower rate (67% of 21 evaluable patients; P = .0034) and durability (P = .0081, hazard radio favoring CDAR, 0.094) of MRD-free CR. Nevertheless, 12 patients in the delayed arm remained MRD free when restaged 6-104 (median, 78) months after last delayed rituximab treatment. Compared with cladribine monotherapy, CDAR led to brief grade 3/4 thrombocytopenia (59% v 9%; P < .0001) and platelet transfusions without bleeding (35% v 0%; P = .0002), but higher neutrophil (P = .017) and platelet (P = .0015) counts at 4 weeks.

CONCLUSION

Achieving MRD-free CR of HCL after first-line cladribine is greatly enhanced by concurrent rituximab and less so by delayed rituximab. Longer follow-up will determine if MRD-free survival leads to less need for additional therapy or cure of HCL.

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.