Biology

The term leukemia means white blood. This term was developed because in former times when chronic leukemias were not effectively treated, instead of having a normal, reddish-purplish color to the blood when it settled, there was a creamy color associated with a marked increase in the white blood cells. Chronic lymphocytic leukemia (CLL) is a slow developing disease. It is characterized by an elevated lymphocyte (white blood cell) count which can cause swollen lymph nodes and enlarged liver and spleen. A normal lymphocyte count averages at 12,000. In CLL patients this level is usually 25,000 to 100,000. The vast majority of CLL cases affect B-cells, a type of lymphocyte. A very small percentage of cases affect T-cells, another type of lymphocyte. Reasons for this divergence are under investigation.

Although the exact cause of CLL is still unknown, it is understood that a defect in the DNA causes an increased production of long-lived, abnormal lymphocytes that refuse to die as normal cells do. These abnormal lymphocytes become CLL cells which are generated in the bone marrow, invade the blood stream and accumulate in organs such as lymph nodes, liver and spleen. With an increased number of abnormal lymphocytes in the body, there is less room for healthy lymphocytes, other types of white blood cells, red blood cells, and platelets.

CLL is traditionally considered an indolent disorder characterized by a stable disease course or slow progression. Although this may be correct compared to acute leukemias or some of the aggressive lymphomas, the biological characteristics and clinical behavior of CLL are far more variable than previously thought. Advances in technology have provided a much better understanding of the variants of CLL. These variants are used as prognostic markers to help determine a patient’s need for treatment and survival outcome. They are also used to verify that the disease is indeed CLL. (Learn about similar lymphoid diseases.)

Technology has also allowed for the discovery of the importance of the CLL microenvironment. This is the environment in which the cells reside. The CLL cells are embedded in a network of other cells and molecules that provide growth and survival capabilities for the CLL cells. The communication between the microenvironment and the CLL cells is essential for their function and survival. It has been concluded that the microenvironment provides resistance to current therapies, making it a hot topic of investigation, both for a better understanding of the interactions with the CLL cells and as a therapeutic target.

In summary, the knowledge of the biology of CLL has grown over the last few years and will continue to rapidly expand. This will provide patients with more individualized care and better treatment options. Where CLL was once thought to be a uniform disease, it is now understood that CLL may follow a rather unpredictable disease course.