Types of Leukemia

There are several types of leukemia. They are grouped in two ways. One way is by how quickly the disease develops and gets worse. The other way is by the type of blood cell that is affected.

Leukemia is either acute or chronic. In acute leukemia, the abnormal blood cells (blasts) remain very immature and cannot carry out their normal functions. The number of blasts increases rapidly, and the disease gets worse quickly. In chronic leukemia, some blast cells are present, but in general, these cells are more mature and can carry out some of their normal functions. Also, the number of blasts increases less rapidly than in acute leukemia. As a result, chronic leukemia gets worse gradually.

Leukemia can arise in either of the two main types of white blood cells — lymphoid cells or myeloid cells. When leukemia affects lymphoid cells, it is called lymphocytic leukemia. When myeloid cells are affected, the disease is called myeloid or myelogenous leukemia.

The disease appears in one of four major forms:

• Acute lymphocytic leukemia
  (ALL) is the most common type of leukemia in young children. This disease also affects adults, especially those age 65 and older.
• Acute myeloid leukemia
  (AML) occurs in both adults and children. This type of leukemia is sometimes called acute nonlymphocytic leukemia (ANLL).
• Chronic lymphocytic leukemia
  (CLL) most often affects adults over the age of 55. It sometimes occurs in younger adults, but it almost never affects children.
• Chronic myeloid leukemia
  (CML) occurs mainly in adults. A very small number of children also develop this disease.