Types of Leukemia
The types of leukemia can be grouped based on how quickly the disease develops and gets worse. Leukemia is either chronic (which usually gets worse slowly) or acute (which usually gets worse quickly):
- Chronic leukemia: Early in the disease, the leukemia cells can still do some of the work of normal white blood cells. People may not have any symptoms at first. Doctors often find chronic leukemia during a routine checkup - before there are any symptoms. Slowly, chronic leukemia gets worse. As the number of leukemia cells in the blood increases, people get symptoms, such as swollen lymph nodes or infections. When symptoms do appear, they are usually mild at first and get worse gradually.
- Acute leukemia: The leukemia cells can't do any of the work of normal white blood cells. The number of leukemia cells increases rapidly. Acute leukemia usually worsens quickly.
The types of leukemia also can be grouped based on the type of white blood cell that is affected. Leukemia can start in lymphoid cells or myeloid cells. See the picture of these cells. Leukemia that affects lymphoid cells is called lymphoid, lymphocytic, or lymphoblastic leukemia. Leukemia that affects myeloid cells is called myeloid, myelogenous, or myeloblastic leukemia.
There are four common types of leukemia:
- Chronic lymphocytic leukemia (CLL): CLL affects lymphoid cells and usually grows slowly. It accounts for more than 15,000 new cases of leukemia each year. Most often, people diagnosed with the disease are over age 55. It almost never affects children.
- Chronic myeloid leukemia (CML): CML affects myeloid cells and usually grows slowly at first. It accounts for nearly 5,000 new cases of leukemia each year. It mainly affects adults.
- Acute lymphocytic (lymphoblastic) leukemia (ALL): ALL affects lymphoid cells and grows quickly. It accounts for more than 5,000 new cases of leukemia each year. ALL is the most common type of leukemia in young children. It also affects adults.
- Acute myeloid leukemia (AML): AML affects myeloid cells and grows quickly. It accounts for more than 13,000 new cases of leukemia each year. It occurs in both adults and children.
Hairy cell leukemia is a rare type of chronic leukemia.
Hairy cell leukemia: A form of chronic leukemia in which malignant B-lymphocytes (a type of white blood cell) are seen in the bone marrow, spleen, and peripheral blood and when viewed under the microscope, these cells appear to be covered with tiny hair-like projections. Hairy cell leukemia represents 2% of all leukemia.
The characteristic features of the disease include marked enlargement of the spleen (splenomegaly), low blood cell counts (pancytopenia), a relatively small number of circulating tumor cells with a hairy appearance, and infiltration of the spleen, liver, and bone marrow by the leukemic hairy cells.
Annexin A1 (ANXA1) is a gene that is unregulated in hairy cell leukemia. ANXA1 protein expression is specific to hairy cell leukemia. Detection of ANXA1 (by immunocytochemical means) provides a simple, highly sensitive and specific assay for the diagnosis of hairy cell leukemia.
Splenectomy (surgical removal of the spleen) provides palliation (some help but not a cure). Treatment is usually with drugs, principally interferon alfa and purine analogues such as cladribine and pentostatin. For resistant cases, a promising immunotoxin has been developed that targets CD22, a molecule expressed exclusively on the surface of B-cells, including virtually all hairy cells.
Hairy cell leukemia was first described in 1958 and was misleadingly called leukemic reticuloendotheliosis.