The US Food and Drug Administration has approved moxetumomab pasudotox for the treatment of adults with relapsed or refractory hairy cell leukemia (HCL) who have received at least two prior systemic therapies, including treatment with a purine nucleoside analog.
Moxetumomab pasudotox is a CD22-directed cytotoxin, and is a first-in-class treatment for HCL. Approval was based on a single-arm phase III clinical trial involving 80 patients with relapsed or refractory HCL who had received at least two prior systemic therapies (including at least one purine nucleoside analog). The trial showed a durable complete response rate of 30% (the proportion of patients maintaining hematologic remission for more than 180 days after achieving a complete response), and an overall response rate of 75% (the proportion of patients with a partial or complete response). 
Approval comes with a black box warning for capillary leak syndrome and hemolytic uremic syndrome, which are potentially life-threatening adverse effects of treatment.
HCL is a rare indolent leukemia that affects B cells, and it can be life-threatening. Around 30% to 40% of patients with HCL relapse after initial treatment.   Few treatments are available for relapsed or refractory HCL, and there is currently no agreed standard of care.See Management: approach See Management: treatment algorithm
A B-cell malignancy that is characterized commonly by symptoms of fatigue, a markedly enlarged spleen, and a distinctive histologic appearance on peripheral blood smear and bone marrow biopsy.
The disease is not curable. However, it is highly responsive to therapy and may be managed successfully for a decade or more.
Patients who are without symptoms do not require immediate treatment; early treatment does not extend life expectancy.
In symptomatic patients, purine analogs have largely replaced traditional therapies, such as splenectomy, except in rare cases of splenic rupture or massive splenomegaly.
Supportive care with antibiotics, nonsteroidal anti-inflammatory drugs, administration of irradiated blood products, and granulocyte colony-stimulating factors may have a role in therapy for hairy cell leukemia.
Hairy cell leukemia (HCL) is an uncommon, indolent, mature B-cell neoplasm. It was described as a distinct clinical entity in 1958.  Seen under the microscope, the cells have delicate cytoplasmic projections, resembling hair, and that is why the disease was named HCL. The disease has a characteristic presentation of pancytopenia, splenomegaly, and circulating hairy cells in blood, marrow, and other hematopoietic organs. 
USF Center for Comparative Effectiveness Research and Evidence Based Medicine
Department of Internal Medicine, College of Medicine
Moffitt Cancer Center & Research Institute, Department of Health Outcomes & Behavior
University of South Florida
AK declares that he has no competing interests.
Division of Hematology-Oncology
Blood and Marrow Transplantation Program
MKD declares that he has no competing interests.
Dr Ambuj Kumar and Dr Mohamed Kharfan-Dabaja would like to gratefully acknowledge Dr Benjamin Djulbegovic, a previous contributor to this topic. BD declares that he has no competing interests.
Section of Haemato-Oncology
Brookes Lawley Institute of Cancer
DC declares that he has no competing interests.
Clinical Professor of Medicine
University of Texas Health Science Center San Antonio
RL declares that he has no competing interests.
Section of Hematology and Oncology
Department of Internal Medicine
Wake Forest University Baptist Medical Center
RC declares that she has no competing interests.
The Royal Marsden Hospital
CD declares that she has no competing interests.
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