Leukemia is classified by how quickly it progresses (chronic or acute) and according to the type of white blood cell that multiplies. When trying to classify the type of leukemia present, doctors check whether it is immune system cells that are multiplying (lymphocytes), bacteria-destroying cells (granulocytes) or macrophage-forming cells (monocytes).
If the abnormal white blood cells are primarily granulocytes or monocytes, the leukemia is categorized as myelogenous, or myeloid, leukemia. If the abnormal blood cells arise from bone marrow lymphocytes, the cancer is called lymphocytic leukemia.
Acute leukemia grows rapidly. It can overrun the body within a few weeks or months. Chronic leukemia, however, is slow-growing and progressively worsens over the years.
Children often develop acute forms of leukemia, which are managed differently than leukemia in adults. Leukemia in childhood presents a set of challenges, because acute leukemia spreads quickly, treatment must be immediate.
In chronic leukemia, the blood-forming cells eventually mature, or differentiate but they are not "normal." They remain in the bloodstream much longer than normal white blood cells and they are unable to combat infection well.
There are four types of leukemia that occur most frequently. These classifications are based upon whether the leukemia is acute versus chronic and myelogenous versus lymphocytic.
The four types are:
* Acute Myelogenous (granulocytic) Leukemia (AML)
* Chronic Myelogenous (granulocytic) Leukemia (CML)
* Acute Lymphocytic (lymphoblastic) Leukemia (AL)
* Chronic Lymphocytic Leukemia (CLL)
The most common form of adult leukemia, affecting mostly men diagnosed at near age 65, is acute myelogenous leukemia (AML)—also known as acute nonlymphocytic leukemia (ANLL). Due to recent positive developments in treatment techniques, AML can be kept in remission (lessening of the disease) in approximately 60 to 70 percent of adults who undergo appropriate therapy. The overall cure rates are somewhere in the 40 to 50 percent range.