Leukemia is a cancer of the blood cells. Leukemia begins when healthy blood cells change and grow out of control. 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:
- Red blood cells that carry oxygen throughout the body
- White blood cells that fight infection
- Platelets, which help the blood to clot
Leukemia is named after the specific blood cell that becomes cancerous, which includes:
- Lymphoid cells. White blood cells mostly found in the lymphoid tissues, such as the spleen, lymph nodes, and tonsils.
- Myeloid cells. These are found in the bone marrow and develop into cells that fight bacterial infections.
There are 4 main types of leukemia in adults:
About PLL and HCL
This section focuses on prolymphocytic leukemia (PLL) and hairy cell leukemia (HCL). These are other, less common types of leukemia, but they are generally subcategories of 1 of the 4 main categories. PLL and HCL are types of chronic B-cell leukemia. B cells are a specific type of lymphocyte that 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 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 hair-like projections 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 fight disease and infection. Eventually, these cells crowd out the healthy cells. Treatment is usually very effective for HCL.