Leukemia Types of Leukemia. Cancer is not a single disease, but rather a group of diseases that cause cells to develop abnormally so that they do not functionproperly. Leukemia is one of these diseases—a cancer of the white blood cells. Leukemia starts in the body’s bone marrowand can spread to other parts of the body. Both children and adults can get leukemia. The exact causes of leukemia are notknown. An article in the August 22/29, 2001, issue of JAMA reports on chronic myelogenous leukemia research and treatment. • Acute lymphocytic leukemia—This type of leukemia develops from cells in the bone marrow called lymphocytes that grow too rapidly and do not mature properly. It can affect children or adults, but is more common in children (about half of all childhoodcases). • Chronic lymphocytic leukemia—This type of leukemia also develops from lymphocytes. The cells in this type of leukemia look mature but some of them are not normal. The cells live too long and cause a buildup of white blood cells. This type occurs almostexclusively in adults and is the most common leukemia found in adults. • Acute myelogenous leukemia—Sometimes called myeloid leukemia, this type develops from either of two types of white blood cells (granulocytes or monocytes). It can occur in either children or adults. • Chronic myelogenous leukemia—Another form of myeloid leukemia, the white blood cells in this type (granulocytes or monocytes) develop abnormally. This type of leukemia is very rare in children but is not uncommon in adults.