Leukemia is cancer of the blood cells. About 31,000 new cases of leukemia are diagnosed in the United States and 3,500 new cases are diagnosed in Canada each year. Leukemia is typically thought to be a childhood disease, but in fact it strikes many more adults. Smoking increases the risk of developing leukemia, as does long-term exposure to high levels of the chemical benzene and high-dose radiation exposure
There are four types of leukemia, classified by the type of blood cell affected and whether the cells are mature or immature. The four major types are acute myelocytic leukemia (AML), chronic myelocytic leukemia (CML), acute lymphocytic leukemia (ALL), and chronic lymphocytic leukemia (CLL). AML and CLL are most common in adults, while ALL is the most common form in children. CML also affects adults. Acute leukemias progress rapidly, while chronic leukemias tend to develop slowly.
Most symptoms of leukemia result from the lack of normal blood cells that occurs when leukemia cells crowd out normal cells. General symptoms include weight loss, fever, and loss of appetite, and less often, profuse bleeding from the gums and mucous membranes under the skin. Low levels of red blood cells may also indicate the presence of leukemia.
Pathologists can distinguish various types of leukemia by the appearance of the cancerous cells underneath a microscope. Hairy cell leukemia, a rare form of chronic lymphocytic leukemia, is characterized by cells with minute, hairlike projections on their surface.
In the United States the five-year survival rate varies according to the type of leukemia and the age of the patient. Almost 68 percent of the people diagnosed with CLL live at least five years. The five-year survival rate for adult ALL is almost 56 percent and is 70 percent for children with ALL. More than 27 percent of those diagnosed with CML survive five years or more. AML is the most fatal of the leukemias. The five-year survival rate for adults with this disease is just over 11 percent, while for children it is 40 percent.