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Cancer Health Center

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Hairy Cell Leukemia Treatment (PDQ®): Treatment - Patient Information [NCI] - General Information About Hairy Cell Leukemia

Hairy cell leukemia is a type of cancer in which the bone marrow makes too many lymphocytes (a type of white blood cell).

Hairy cell leukemia is a cancer of the blood and bone marrow. This rare type of leukemia gets worse slowly or does not get worse at all. The disease is called hairy cell leukemia because the leukemia cells look "hairy" when viewed under a microscope.

Anatomy of the bone. The bone is made up of compact bone, spongy bone, and bone marrow. Compact bone makes up the outer layer of the bone. Spongy bone is found mostly at the ends of bones and contains red marrow. Bone marrow is found in the center of most bones and has many blood vessels. There are two types of bone marrow: red and yellow. Red marrow contains blood stem cells that can become red blood cells, white blood cells, or platelets. Yellow marrow is made mostly of fat.

Leukemia may affect red blood cells, white blood cells, and platelets.

Normally, the bone marrow makes blood stem cells (immature cells) that become mature blood cells over time. A blood stem cell may become a myeloid stem cell or a lymphoid stem cell.

A myeloid stem cell becomes one of three types of mature blood cells:

  • Red blood cells that carry oxygen and other substances to all tissues of the body.
  • White blood cells that fight infection and disease.
  • Platelets that form blood clots to stop bleeding.

A lymphoid stem cell becomes a lymphoblast cell and then into one of three types of lymphocytes (white blood cells):

  • B lymphocytes that make antibodies to help fight infection.
  • T lymphocytes that help B lymphocytes make antibodies to help fight infection.
  • Natural killer cells that attack cancer cells and viruses.

Blood cell development. A blood stem cell goes through several steps to become a red blood cell, platelet, or white blood cell.

In hairy cell leukemia, too many blood stem cells become lymphocytes. These lymphocytes are abnormal and do not become healthy white blood cells. They are also called leukemia cells. The leukemia cells can build up in the blood and bone marrow so there is less room for healthy white blood cells, red blood cells, and platelets. This may cause infection, anemia, and easy bleeding. Some of the leukemia cells may collect in the spleen and cause it to swell.

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