Definition
Leukemia is a cancer of the blood cells. A progressive, malignant disease of the blood-forming organs, characterized by distorted proliferation and development of leukocytes and their precursors in the blood and bone marrow. Leukemias were originally termed acute or chronic based on life expectancy but now are classified according to cellular maturity. Acute leukemias consist of predominately immature cells; chronic leukemias are composed of more mature cells.
Description
Acute Leukemia
With acute leukemia, immature blood cells reproduce quickly in the bone marrow, where they eventually crowd out healthy cells. When present in high numbers, these immature, abnormal cells sometimes can spread to other organs, causing damage, especially in a type of leukemia called acute myeloid leukemia. The two main types of acute leukemia involve different types of blood cells:
- Acute myeloid leukemia accounts for 50% of leukemia diagnosed in teenagers and in people in their 20s. It is the most common acute leukemia in adults. It occurs when primitive blood-forming cells called myeloblasts reproduce without developing into normal blood cells. Immature myeloblast cells crowd the bone marrow and interfere with the production of healthy normal blood cells. This leads to anemia (not having enough red blood cells), bleeding and bruising (due to a lack of blood platelets, which help the blood to clot), and frequent infections because there are not enough protective white blood cells.
- Acute lymphoid leukemia is the most common type of leukemia that affects children, mainly those younger than 10. Adults sometimes develop acute lymphoid leukemia, but it is rare in people older than 50. It occurs when primitive blood-forming cells called lymphoblasts reproduce without developing into normal blood cells. These abnormal cells crowd out healthy blood cells. They can collect in the lymph nodes and cause swelling.
Chronic Leukemia
Chronic leukemia is when the body produces too many blood cells that have developed part way but often cannot function like mature blood cells. Chronic leukemia usually develops more slowly and is a less dramatic illness than acute leukemia. There are two main types of chronic leukemia:
- Chronic myeloid leukemia occurs most often in people between ages 25 and 60. In this form of leukemia, the abnormal cells are a type of blood cell called myeloid cells. Chronic myeloid leukemia cells usually involve an abnormality in the genetic code called the Philadelphia chromosome. However, this disease is not an inherited defect. Chronic myeloid leukemia sometimes can be cured with a bone marrow transplant.
- Chronic lymphoid leukemia is rare in people younger than 30. It is more likely to develop the older a person gets. The greatest number of cases occur in people between ages 60 and 70. In this form of leukemia, the abnormal cells in the bone marrow are a type of blood cell called lymphocytes. These abnormal cells cannot fight infection as well as normal cells can. With chronic lymphoid leukemia, cancerous cells live in the bone marrow, blood, spleen and lymph nodes, where they cause swelling that appears as swollen glands.
The vast majority of leukemias occur in people without any family history of leukemia and are not believed to be inherited. However, some forms of the disease, especially chronic lymphoid leukemia, occasionally strike close relatives in the same family. Certain genetic abnormalities (such as Down syndrome) have been linked to the development of specific forms of leukemia. In cases of myeloid leukemia, an increased risk of the illness has been linked to excessive exposure to radiation and to heavy exposure to benzene, a chemical found in unleaded gasoline.