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 white blood cells involved in the immune system of the body. In some people having CLL, the disease grows and progresses slowly, which means it can take several years for symptoms to appear or for treatment to be done. Some patients may never require treatment for their CLL. In other patients, the disease grows more quickly and requires treatment sooner.
Lymphocytes travel in the bloodstream and are made in four places in the body-
- Lymph nodes are the tiny, bean-shaped organs that fight infection
- Spleen also filters the blood
- The thymus is an organ under the breast bone
- Bone marrow, the red, spongy tissue in the inner part of the large and flat bones
There are three different types of lymphocytes-
- T cells fight infection by triggering other cells in the immune system and by killing infected cells
- B cells make antibodies
- Natural killer cells fight microbes and cancer cells
In people having CLL, the abnormal cells crowd other types of cells in the bone marrow. This crowding prevents the production of healthy blood cells, including:
- Red blood cells that carry oxygen
- Different types of white blood cells, like neutrophils or granulocytes that fight infection
- Platelets are needed for blood to clot
This means that people having CLL may have anemia from low red blood cells and more infections because they don’t have enough white blood cells. They may also bruise or bleed more quickly because of a low level of platelets.
CLL is often diagnosed when too many abnormal lymphocytes are found in the blood, known as lymphocytosis. However, the same disease can occur when the abnormal lymphocytes are primarily in the lymph nodes but not present in the blood. This is called small lymphocytic lymphoma, but it behaves very similar to CLL.
Types of CLL
There are two general types of CLL based on whether the disease affects B cells or T cells. Doctors need to determine 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. Around 1% of people with CLL have the T-cell type.
However, several subtypes differ at the genetic level between these two types of CLL. This means that the disease can act differently based on the genetic subtype. For instance, one person with the B-cell type may have the disease act differently than another person with the B-cell type.