What is Hairy Cell Leukemia (HCL)?

From the Guidelines

Hairy cell leukemia is a rare, slow-growing blood cancer that requires prompt diagnosis and treatment to improve morbidity, mortality, and quality of life, with the standard first-line therapy being a purine analog, either cladribine or pentostatin, as recommended by the most recent guidelines 1. The diagnosis of hairy cell leukemia is established through morphological evaluation of peripheral blood smears, bone marrow biopsy with or without aspirate, and adequate immunophenotyping by immunohistochemistry or flow cytometry, as outlined in the NCCN clinical practice guidelines 1. Key considerations in the diagnosis and management of hairy cell leukemia include:

• Complete blood count and peripheral blood smear review to identify leukemic cells
• Immunophenotypic analysis by flow cytometry to confirm diagnosis
• Bone marrow aspiration and trephine biopsy to assess extent of bone marrow involvement
• Identification of the BRAF V600E mutation, which is present in most patients with classic hairy cell leukemia 1
• Regular monitoring with blood counts and periodic bone marrow examinations to manage disease and prevent relapse In terms of treatment, the use of targeted and non-immunosuppressive agents as first-line treatment for hairy cell leukemia is now recommended, particularly in the context of the COVID-19 pandemic, to minimize the risk of severe infection 1. Additional treatment options for relapsed disease include:
• Repeated use of purine analogs
• Targeted therapies like rituximab or BRAF inhibitors, particularly in patients with the BRAF V600E mutation
• Interferon alpha, which is now reserved for special situations
• Splenectomy, which is rarely performed today but may help relieve symptoms in select cases 1

From the Research

Definition and Types of Leukemia

• Leukemia is a clonal proliferation of hematopoietic stem cells in the bone marrow 2
• The four broad subtypes of leukemia are acute lymphoblastic, acute myelogenous, chronic lymphocytic, and chronic myelogenous 2

Hairy Cell Leukemia

• Hairy cell leukemia (HCL) is a chronic B-cell malignancy with multiple treatment options 3
• Treatment options for HCL include purine analogs, moxetumomab pasudotox, vemurafenib, dabrafenib, trametinib, and ibrutinib 3
• HCL variant (HCLv) is also a type of hairy cell leukemia, and its treatment strategies are similar to those of HCL 3

Acute Lymphoblastic Leukemia

• Acute lymphoblastic leukemia (ALL) is the second most common acute leukemia in adults, with an incidence of over 6500 cases per year in the United States alone 4
• The hallmark of ALL is chromosomal abnormalities and genetic alterations involved in differentiation and proliferation of lymphoid precursor cells 4
• Treatment of ALL includes multi-agent chemotherapy, vincristine, corticosteroids, and an anthracycline, with allogeneic stem cell transplantation for eligible candidates 4

Treatment and Prognosis

• Allogeneic stem-cell transplantation with sequential conditioning has shown promising results in relapsed/refractory acute lymphoblastic leukemia (RR-ALL) 5
• Novel therapies, including BITE antibodies, inotuzumab, and CAR-T cells, are being developed to improve outcomes in patients with RR-ALL 5
• The prognosis of patients with leukemia varies depending on the subtype, age, and response to treatment, with five-year survival rates being highest in younger patients and in patients with chronic myelogenous leukemia or chronic lymphocytic leukemia 2