Definition of Chronic lymphocytic leukemia (CLL):

Chronic lymphocytic leukemia is cancer of the white blood cells (lymphocytes).

Causes, incidence, and risk factors:

Chronic lymphocytic leukemia (CLL) causes a slow increase in the number of B lymphocytes in the bone marrow. The cancerous cells spread from the blood marrow to the blood, and can also affect the lymph nodes and other organs. CLL causes the bone marrow to fail and weakens the immune system.

The reason for this increase in B lymphocytes is unknown. There is no link to radiation, cancer-causing chemicals, or viruses.

Usually, the symptoms develop gradually. Many cases are detected by routine blood tests in people with no symptoms.

CLL primarily strikes adults. The average age of a patient with this type of leukemia is 70. It is rarely seen in people younger than 40. The disease is more common in Jewish people of Russian or East European descent, and is uncommon in Asia.