Editorial Note: Please note that this section is currently under review and will be updated soon.
ON THIS PAGE: You will find some basic information about this disease and the parts of the body it may affect. This is the first page of Cancer.Net’s Guide to Chronic Lymphocytic Leukemia. Use the menu to see other pages. Think of that menu as a roadmap for this complete guide.
Leukemia is a cancer of the blood. Leukemia begins when healthy blood cells change and grow out of control. Chronic lymphocytic leukemia (CLL) is a cancer of the lymphocytes. Lymphocytes are a type of white blood cell involved in the body’s immune system. In some people with CLL, the disease grows and progresses slowly. This means it may take years for symptoms to appear or for treatment to be needed. In fact, some patients may never need treatment for their CLL. In other patients, the disease grows more quickly and needs treatment sooner.
Lymphocytes circulate in the bloodstream and are made in 4 places in the body:
Lymph nodes, which are the tiny, bean-shaped organs that fight infection
Spleen, which also filters the blood
Thymus, an organ under the breast bone
Bone marrow, the spongy, red tissue in the inner part of the large and flat bones
There are 3 different types of lymphocytes:
T cells, which fight infection by triggering other cells in the immune system and by destroying infected cells
B cells, which make antibodies
Natural killer (NK) cells, which fight microbes and cancer cells
In people with CLL, the abnormal cells crowd other types of cells in the bone marrow. This crowding prevents the production of the healthy blood cells, including:
Red blood cells that carry oxygen
Other types of white blood cells, such as neutrophils or granulocytes that fight infection
Platelets, which are needed for blood to clot
This means that people with CLL may have anemia from low levels of red blood cells and more infections because they do not have enough white blood cells. They may also bruise or bleed more easily because of a low level of platelets.
Most often, CLL is diagnosed when too many abnormal lymphocytes are found in the blood, also known as lymphocytosis. However, the same disease can occur when the abnormal lymphocytes are mostly in the lymph nodes but not in the blood. This is called small lymphocytic lymphoma, but it behaves very similarly to CLL.
Types of CLL
There are 2 general types of CLL based on whether the disease affects B cells or T cells. It is important for doctors to find out whether the disease is caused by the overgrowth of T cells or B cells.
B-cell CLL. More than 95% of people with CLL have the B-cell type. And, about 1% of people with B-cell leukemia have a type called B-cell prolymphocytic leukemia (PLL).
T-cell prolymphocytic leukemia. The T-cell type of CLL is now called T-cell prolymphocytic leukemia. About 1% of people with CLL have the T-cell type.
However, even between these 2 types of CLL, there are several subtypes that differ at the genetic level. This means that the disease may act differently based on the genetic subtype. For example, one person with the B-cell type may have the disease act differently than another person with the B-cell type.
Learn more about other, rare types of chronic T-cell leukemia and types of B-cell leukemia.
Looking for More of an Introduction?
If you would like more of an introduction, explore these related items. Please note that these links will take you to other sections on Cancer.Net:
Cancer.Net Patient Education Video: View a short video led by an ASCO expert in leukemia that provides basic information and areas of research.
Cancer.Net En Español: Read about CLL in Spanish. Infórmase sobre leucemia linfocítica crónica en español.
The next section in this guide is Statistics. It helps explain the number of people who are diagnosed with CLL and general survival rates. Use the menu to choose a different section to read in this guide.