Leukemia is a cancer of the bone marrow and blood. It is characterized by the uncontrolled accumulation of blood cells. Leukemia is divided into four categories: myelogenous or lymphocytic, each of which can be acute or chronic. The terms myelogenous or lymphocytic describe the cell type involved.
There are four major types of leukemia.
Acute Myelogenous Leukemia (AML)
Acute Lymphocytic Leukemia (ALL)
Chronic Myelogenous Leukemia (CML)
Chronic Lymphocytic Leukemia (CLL)
Lymphocytic: Referring to lymphocytes, a type of white blood cell.
Myelogenous: Originating in or produced by the bone marrow
These cell changes take place in a type of marrow cell that normally goes on to form red cells, some types of white cells, and platelets.
ALL and AML are each composed of blast cells, known as lymphoblasts or myeloblasts. Acute leukemias progress rapidly without treatment.
Chronic leukemias have few or no blast cells. CLL and CML usually progress slowly compared to acute leukemias.
In AML and ALL the original acute leukemia cell goes on to form about a trillion more leukemia cells. These cells are described as "nonfunctional" because they do not work like normal cells and they crowd out the normal cells in the marrow which causes a decrease in the number of new normal cells made in the marrow. This results in low red cell counts while the lack of normal white cells impairs the body's ability to fight infections. A shortage of platelets results in bruising and easy bleeding.
In CML the leukemia cell that starts the disease makes red and white blood cells and platelets that function almost like normal cells. The number of red cells is usually reduced, resulting in anemia while many white cells and sometimes many platelets are still made. Even though the white cells behave almost normally, their counts are high and continue to rise. If left untreated, the white cell count can continue to rise so high that blood flow slows down and anemia becomes severe.
In CLL the leukemia cell that starts the disease produces too many lymphocytes that do not function. These cells replace normal cells in the marrow and lymph nodes which weakens the patient's immune response. The high number of leukemia cells in the marrow may crowd out normal blood-forming cells and lead to a low red cell count and can also lead to low neutrophil and platelet counts.
Unlike the other three types of leukemia, some patients with CLL may have very little to no progression for a long time and remain in good health without treatment for long periods of time.
A CBC is used to diagnose leukemia. This is a blood test that may show high or low levels of white cells and show the presence of leukemic cells. Sometimes, platelet counts and red cell counts are also low. Bone marrow aspiration or bone marrow biopsy are often done to confirm the diagnosis and to look for chromosome abnormalities. These tests help to identify the leukemia cell-type. These tests are usually repeated after treatment begins to measure how well the treatment is working or in the case of a non-progressing CLL, to watch for changes that would indicate the beginning of progression.