Hairy cell leukemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Haytham Allaham, M.D. [2], James Nasr[3]; Grammar Reviewer: Natalie Harpenau, B.S.[4]
Overview
Hairy cell leukemia arises from B cells, that are normally involved in the process of human immunoglobulins production. The most common gene involved in the pathogenesis of hairy cell leukemia is a BRAF V600E mutation. On microscopic histopathological analysis, characteristic findings of hairy cell leukemia include small cells with "fried egg"-like appearance, well-demarcated thread-like cytoplasmic extensions, and a clear cytoplasm. Hairy cell leukemia is found to approximately comprise 1.4% of all lymphomas. The incidence of hairy cell leukemia is approximately 2.8-3.0 per 1,000,000 individuals in the United States. The incidence of hairy cell leukemia increases with age; the median age at diagnosis is 55-60 years. Males are more commonly affected with hairy cell leukemia than females. The male to female ratio is approximately 4 to 1. Studies have proposed a number of risk factors for the development of hairy cell leukemia such as certain chemicals exposure, radiation exposure, and UV light exposure. Symptoms of hairy cell leukemia include fever, night sweats, and weight loss. Physical examination of patients with hairy cell leukemia is usually remarkable for pallor, petechiae, and splenomegaly. Laboratory findings consistent with the diagnosis of hairy cell leukemia include abnormal complete blood count, immunohistochemistry, and flow cytometry. The presence of hairy cells with thread-like cytoplasmic extensions on blood smear is a key diagnostic feature among patients with hairy cell leukemia. Hairy cell leukemia is a chronic, highly treatable malignancy with prolonged remission achievable in most patients. The mainstay of therapy for hairy cell leukemia patients is chemotherapy. Pharmacological agents used for the treatment of hairy cell leukemia patients include cladribine, pentostatin, rituximab, and vemurafenib.
Historical Perspective
The term hairy cell leukemia was first used to describe the malignancy by Dr. R. Schrek and Dr. W. J. Donnelly, in 1966.
Classification
Hairy cell leukemia is a distinct indolent, small, mature B-cell neoplasm.
Pathogenesis
Hairy cell leukemia arises from B cells that are normally involved in the process of human immunoglobulins production. It is thought to originate from a peripheral, antigen-experienced mature B cell with features resembling post–germinal center memory B cells. The most common gene involved in the pathogenesis of hairy cell leukemia is BRAF V600E mutation. On microscopic histopathological analysis, characteristic findings of hairy cell leukemia include small cells with "fried egg" like appearance, well-demarcated thread-like cytoplasmic extensions, and a clear cytoplasm. Hairy cell leukemia is driven by constitutive activation of the RAF–MEK–ERK signalling pathway which inhibits apoptosis and drives survival.
Causes
Hairy cell leukemia may be caused by mutations in the BRAF gene.
Epidemiology and Demographics
Hairy cell leukemia is relatively rare, accounting for 1.4% of all lymphomas. The incidence of hairy cell leukemia is approximately 2.8-3.0 per 1,000,000 individuals in the United States. The incidence of hairy cell leukemia increases with age. The median age range at diagnosis of hairy cell leukemia is 55 to 60 years. Males are more commonly affected with hairy cell leukemia than females. The male to female ratio is approximately 4 to 1.
Risk Factors
The most potent risk factor in the development of hairy cell leukemia is chemical exposure. Other risk factors include radiation exposure, and UV light exposure.
Screening
According to the the U.S. Preventive Service Task Force (USPSTF), there is insufficient evidence to recommend routine screening for hairy cell leukemia.
Natural History
Most patients with hairy cell leukemia are asymptomatic at the time of diagnosis. If left untreated, most of the patients with hairy cell leukemia will gradually develop anemia, recurrent infections, and recurrent bleeding. The complications of hairy cell leukemia are mainly due to bone marrow failure.
Diagnosis
Staging
There is no established system for the staging of hairy cell leukemia.
History and Symptoms
A positive history of splenomegaly or cytopenias is suggestive of hairy cell leukemia. The most common symptoms of hairy cell leukemia include weakness, fatigue, gingival bleeding, epistaxisand menorrhagia.
Physical Examination
Physical examination of patients with hairy cell leukemia is usually remarkable for pallor, petechiae, and splenomegaly.
Laboratory Findings
Laboratory findings consistent with the diagnosis of hairy cell leukemia include abnormal complete blood count, immunohistochemistry, and flow cytometry. The presence of hairy cells with thread-like cytoplasmic extensions on blood smear is a key diagnostic feature among patients with hairy cell leukemia.
CT Scan
Abdominal CT scan may be helpful in the diagnosis of hairy cell leukemia. The presence of splenomegaly on CT scan is suggestive of hairy cell leukemia.
MRI
MRI of the femur may be helpful in the diagnosis of hairy cell leukemia. Diffuse hyper-intense lesions on T2-weighted MRI image is suggestive of bone marrow infiltration by malignant leukemic cells.
Medical Therapy
Hairy cell leukemia is a chronic, highly treatable malignancy with prolonged remission achievable in most patients. The mainstay of therapy for hairy cell leukemia patients is chemotherapy. Pharmacological agents used for the treatment of hairy cell leukemia patients include cladribine, pentostatin, rituximab, and vemurafenib.
Surgery
The predominant therapy for hairy cell leukemia is chemotherapy. Surgical management, such as splenectomy, may be required in certain cases.