Hairy Cell Leukemia

(HCL; Leukemic Reticuloendotheliosis)


Hairy cell leukemia (HCL) is a rare, slow-growing blood cancer. It affects white blood cells called B lymphocytes. White blood cells protect the body from infection. HCL cells look hairy. Illness happens when these cells build up in the bone marrow and spleen.

White Blood Cells

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Leukemia starts in the bone marrow where blood cells are made. It happens when certain blood cells divide without control or order. The abnormal cells crowd out the healthy blood cells. This causes many of the symptoms.

The cause of HCL is not clear. It may be linked to changes in a gene.

Risk Factors

HCL is more common in men and people over 50 years old.


There may be no symptoms at first. Symptoms of HCL usually develop slowly over time.

They may include:

  • Belly swelling
  • Fever
  • Night sweats
  • Easy bruising
  • Painless lumps in the neck, underarms, stomach, or groin


The doctor will ask about your symptoms and health history. A physical exam will be done.

Tests may be done, such as:

  • Blood tests—to look at blood cell counts
  • Bone marrow biopsy—a sample of bone marrow is taken and tested

Images may be taken of bodily structures with a CT scan.


The treatment of HCL depends on symptoms. HCL is a slow-growing cancer. Treatment may not be needed at first. As HCL progresses, treatment may include:

  • Splenectomy—surgery to remove an enlarged spleen
  • Blood transfusion—to replace low numbers of blood cells
  • Chemotherapy drugs by mouth, injection, or IV— to kill cancer cells
  • Medicines to help the body fight the hairy cells
  • Antibiotics or other medicines to fight infection


There are no current guidelines to prevent HCL.


American Cancer Society
The Leukemia and Lymphoma Society


Canadian Cancer Society
Provincial Health Services Authority


General information about hairy cell leukemia treatment. National Cancer Institute website. Available at: Accessed March 25, 2021.
Hairy cell leukemia. EBSCO DynaMed website. Available at: Accessed March 25, 2021.
Hairy cell leukemia. Leukemia & Lymphoma Society website. Available at:
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Accessed March 25, 2021.
Sarvaria A, Topp Z, et al. Current therapy and new directions in the treatment of hairy cell leukemia: a review. JAMA Oncol. 2016;2(1):123-9.
Treating hairy cell leukemia. American Cancer Society website. Available at: Accessed March 25, 2021.
Last reviewed January 2021 by EBSCO Medical Review Board Mohei Abouzied, MD, FACP
Last Updated: 3/25/2021

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