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Leukemia is a cancer of the blood cells. Leukemia begins when normal blood cells change and grow uncontrollably. Blood cells are made in the bone marrow, the spongy tissue inside the larger bones in the body. There are different types of blood cells, including red blood cells that carry oxygen throughout the body, white cells that fight infection, and platelets that help the blood to clot. Types of leukemia are named after the specific blood cell that becomes cancerous, such as the lymphoid cells (white blood cells of the immune system) or the myeloid cells (cells of the bone marrow which develop into cells that fight bacterial infections). There are four main types of leukemia in adults:
- Acute lymphocytic leukemia (ALL)
- Chronic lymphocytic leukemia (CLL)
- Acute myeloid leukemia (AML)
- Chronic myeloid leukemia (CML)
About PLL and HCL
There are other, less common types of leukemia, but they are generally subcategories of one of the four main categories. This section focuses on prolymphocytic leukemia (PLL) and hairy cell leukemia (HCL), both of which are chronic B-cell leukemias. B cells are a specific type of lymphocyte that normally make antibodies for the immune system.
In PLL, many immature lymphocytes, or prolymphocytes, are found in the blood. This type of leukemia may occur by itself, together with CLL, or CLL may turn into into PLL. PLL tends to worsen more quickly than CLL.
HCL is a slow-growing form of leukemia. It is called “hairy cell” because the abnormal lymphocytes have projections that look like hair when seen under a microscope. As these cells multiply, they build up in the bone marrow, blood, and spleen. Because these lymphocytes are abnormal, they do not work normally to fight disease and infection, and eventually may crowd out the normal cells. Treatment is often very effective for HCL.
Find out more about basic cancer terms used in this section.
Looking for More of an Overview?
If you would like additional introductory information, explore these related items on Cancer.Net:
- ASCO Answers Fact Sheet: Read a one-page fact sheet (available in PDF) that offers an easy-to-print introduction for CLL.
- Cancer.Net Patient Education Video: View a short video led by an ASCO expert in leukemia that provides basic information and areas of research.
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