What is leukemia? What are the different types of leukemia?
Leukemia is a malignancy (cancer) of blood cells. In leukemia, abnormal blood cells are produced in the bone marrow. Usually, leukemia involves the production of abnormal white blood cells -- the cells responsible for fighting infection. However, the abnormal cells in leukemia do not function in the same way as normal white blood cells. The leukemia cells continue to grow and divide, eventually crowding out the normal blood cells. The end result is that it becomes difficult for the body to fight infections, control bleeding, and transport oxygen.
There are different types of leukemia, based upon how quickly the disease develops and the type of abnormal cells produced. Leukemia is called an acute leukemia if it develops rapidly. Large numbers of leukemia cells accumulate very quickly in the blood and bone marrow, leading to symptoms such as tiredness, easy bruising, and susceptibility to infections. Acute leukemia requires fast and aggressive treatment.
There are around 62,000 new cases of leukemia each year in the U.S. and about 24,500 deaths due to leukemia. Leukemia makes up about 3.7% of all new cancer cases.
Chronic leukemias develop slowly over time. These leukemias may not cause specific symptoms at the beginning of their course. If left untreated, the cells may eventually grow to high numbers, as in acute leukemias causing similar symptoms.
Leukemias are further classified as myeloid or lymphoid, depending upon the type of white blood cell that makes up the leukemia cells. A basic understanding of the normal development of blood cells is needed to understand the different types of leukemia. Normal blood cells develop from stem cells that have the potential to become many cell types. Myeloid stem cells mature in the bone marrow and become immature white cells called myeloid blasts. These myeloid blasts further mature to become either red blood cells, platelets, or certain kinds of white blood cells. Lymphoid stem cells mature in the bone marrow to become lymphoid blasts. The lymphoid blasts develop further into T or B lymphocytes, special types of white blood cells. Myeloid leukemias are made up of cells that arise from myeloid cells, while lymphoid leukemias arise from lymphoid cells. Knowing the type of cell involved in leukemia is important in choosing the appropriate treatment.
Common types of leukemia
The four most common types of leukemia are acute lymphocytic leukemia, chronic lymphocytic leukemia, acute myeloid leukemia, and chronic myeloid leukemia.
- Acute lymphocytic leukemia (ALL, also known as acute lymphoblastic leukemia) is the most common type of leukemia in children, but it can also affect adults. In this type of leukemia, immature lymphoid cells grow rapidly in the blood. It affects over 6,000 people per year in the U.S.
- Acute myeloid leukemia (AML, also called acute myelogenous leukemia) involves the rapid growth of myeloid cells. It occurs in both adults and children and affects about 21,000 people each year in the U.S.
- Chronic lymphocytic leukemia (CLL) is a slow-growing cancer of lymphoid cells that usually affects people over 55 years of age. It is estimated to affect about 20,000 people in the U.S. every year. It almost never occurs in children or adolescents.
- Chronic myeloid leukemia (CML, also known as chronic myelogenous leukemia) primarily affects adults and occurs in about 8.950 people every year in the U.S.
Less common types of leukemia account for about 6,000 cases of leukemia each year in the U.S.
- Hairy cell leukemia is an uncommon type of chronic leukemia.
- Chronic myelomonocytic leukemia (CMML) is another type of chronic leukemia that develops from myeloid cells.
- Juvenile myelomonocytic leukemia (JMML) is a type of myeloid leukemia that usually occurs in children under 6 years of age.
- Large granular lymphocytic leukemia (LGL leukemia) is a type of chronic leukemia that develops from lymphoid cells. It can be slow- or fast-growing.
- Acute promeylocytic leukemia (APL) is a subtype of AML.