Chronic lymphocytic leukemia (CLL) develops in a specific type of white blood cell called the lymphocyte, which is formed in the bone marrow. These cells migrate from the bone marrow into the blood stream, and then spread throughout the body. Chronic leukemias build slowly over time, and may produce no symptoms for several years, until they spread to other parts of the body including the lymph nodes, liver, and spleen. This type of chronic leukemia produces cells that are not quite mature enough to fight infection as well as normal cells do.
The main differences between chronic and acute lymphocytic leukemia are that the chronic type occurs over a longer period of time and is harder to treat.
Leukemia and lymphoma affect the same white blood cells, but in lymphocytic leukemia the cancer cells are found mostly in the bone marrow and blood stream, while in lymphoma they migrate to different organs in the body, but mainly lymph nodes. Some rare types of leukemia share characteristics of CLL, including:
- Prolymphocytic leukemia (PLL).
- Large granular lymphocyte (LGL) leukemia.
- Hairy cell leukemia (HCL).
Myeloid leukemias (also known as myelocytic, myelogenous, or non-lymphocytic leukemias) start in immature myeloid cells which have the ability to mature into red blood cells, platelet-making cells (megakaryocytes), and white blood cells other than lymphocytes. This type of leukemia forms cells called granulocytes that remain immature and do not function like normal immune cells.
There are very few known risk factors for chronic lymphocytic leukemia (CLL). They include:
- Exposure to certain chemicals – Agent Orange (a chemical weapon used during the Vietnam War) and some pesticides used in farming can increase risk of CLL.
- Family history – first-degree relatives of CLL patients have more than twice the risk of developing CLL.
- Gender – it is more common in males than in females.
- Race/ethnicity – it is more common in Europe and North America than in Asia.
 Franca Fagioli M.D. Antonio Cuneo M.D. Nadia Piva M.D. Maria Gretel Carli Ph.D. Rita Previati M.D. Massimo Balboni M.D. Paolo Tomasi M.D. Daniele Cariani M.D. Gianluigi Scapoli M.D. Gianluigi Castoldi M.D., “Distinct cytogenetic and clinicopathologic features in acute myeloid leukemia after occupational exposure to pesticides and organic solvents.” Wiley Online Library, June, 2006.