hairy cell leukemia

hairy cell leukemia
Name	Hairy cell leukemia
Caption	A blood smear showing characteristic lymphocytes with cytoplasmic projections.
Field	Hematology, Oncology
Symptoms	Fatigue, fever, splenomegaly, pancytopenia
Complications	Infection, bleeding
Onset	Typically middle age
Duration	Chronic
Types	Classic variant, variant form
Causes	Unknown
Risks	Ionizing radiation, herbicide exposure
Diagnosis	Blood test, bone marrow biopsy, immunophenotyping
Differential	Splenic marginal zone lymphoma, chronic lymphocytic leukemia
Prevention	None known
Treatment	Cladribine, pentostatin, rituximab
Prognosis	Generally good with treatment
Frequency	~1,000 new cases annually in the United States
Deaths	Rare with modern therapy

hairy cell leukemia is a rare, indolent B-cell lymphoproliferative disorder characterized by the accumulation of abnormal lymphocytes in the bone marrow, spleen, and peripheral blood. First described in 1958 by Bertha Bouroncle and colleagues at the Ohio State University, it is named for the hair-like cytoplasmic projections visible on the malignant cells under microscopy. The disease typically presents with pancytopenia and splenomegaly, and while its cause remains unknown, associations with ionizing radiation and certain chemical agents have been suggested. Management has been revolutionized since the 1980s by the introduction of purine analogues, which induce durable remissions in most patients.

Signs and symptoms

Patients often present with symptoms related to bone marrow failure and splenomegaly. Common manifestations include profound fatigue, unexplained fever, and night sweats, which are part of a systemic inflammatory response. Splenomegaly is palpable in over 80% of cases and can cause early satiety or left upper quadrant abdominal pain. Due to pancytopenia, patients are at risk for infection from neutropenia, bleeding from thrombocytopenia, and anemia-related dyspnea and pallor. Less common features include hepatomegaly, lymphadenopathy, and autoimmune disorders such as vasculitis or polyarteritis nodosa.

Diagnosis

Diagnosis requires integration of peripheral blood findings, bone marrow biopsy, and immunophenotyping. Examination of a blood smear typically reveals the classic "hairy cells" with filamentous cytoplasmic projections. Flow cytometry is essential, showing a characteristic immunophenotype positive for CD20, CD22, CD11c, CD25, CD103, and annexin A1. A bone marrow biopsy often shows a "dry tap" due to reticulin fibrosis and infiltration by the malignant cells. Molecular genetics may reveal a high prevalence of the BRAF V600E mutation, which is highly specific and aids in distinguishing it from other B-cell lymphomas like splenic marginal zone lymphoma.

Pathophysiology

The disease originates from a mature, post-germinal center B cell that acquires the activating BRAF V600E mutation in the vast majority of classic cases. This mutation constitutively activates the MAPK/ERK pathway, leading to uncontrolled cell proliferation and inhibition of apoptosis. The malignant cells accumulate in the bone marrow and spleen, where they interact with the stromal microenvironment via adhesion molecules like CD44 and VLA-4. This interaction, along with the secretion of fibroblast growth factor, contributes to the characteristic reticulin fibrosis and cytopenia by disrupting normal hematopoiesis.

Treatment

First-line therapy consists of a single course of a purine analogue, either cladribine or pentostatin, which achieves complete remission in over 85% of patients. For relapsed or refractory disease, options include retreatment with a purine analogue, the monoclonal antibody rituximab (often combined with a purine analogue), or the BRAF inhibitor vemurafenib. Splenectomy was historically the primary treatment but is now reserved for rare cases of splenic rupture or refractory cytopenia. Interferon-alpha was an early systemic therapy but is seldom used today.

Prognosis

The prognosis is excellent with modern therapies, with a life expectancy approaching that of the general population. Most patients achieve a prolonged first remission lasting a decade or more. Even upon relapse, effective salvage therapies are available. Long-term complications can include an increased risk of secondary malignancies, such as non-Hodgkin lymphoma or skin cancer, possibly related to therapy or the underlying immune dysfunction. Regular follow-up with a hematologist is recommended to monitor for relapse and manage late effects.

Epidemiology

Hairy cell leukemia accounts for about 2% of all leukemias, with an estimated annual incidence of 3 per 1,000,000 people in the United States. It predominantly affects middle-aged males, with a male-to-female ratio of approximately 4:1. The median age at diagnosis is 55 years. While no clear hereditary pattern exists, some studies suggest a potential link to exposure to ionizing radiation, agricultural chemicals, and sawdust, though evidence remains inconclusive. The variant form of the disease is even rarer and has a distinct clinical and immunophenotypic profile.

Category:Leukemias Category:Rare cancers Category:Hematology