Causes and Risk Factors
Doctors don't know why some cells become leukemic cells and others don't. For most people who have acute lymphoblastic leukemia (ALL), there are no obvious reasons why they developed the disease.
Few risk factors are associated with the disease. Exposure to high doses of radiation therapy used to treat other types of cancer is one known risk factor. Researchers continue to study other possible risk factors. They've found that ALL occurs at different rates in different parts of the world: More developed countries and higher socioeconomic groups tend to have higher ALL rates. This has led researchers to explore ALL's relationship with certain lifestyle, economic and environmental factors, but they have not reached any firm conclusions, which suggests that many factors may be involved. A child who has had multiple diagnostic x-rays may be at a slightly increased risk for ALL; however, more studies need to be done to confirm these research findings. Currently, there's no way to prevent the disease. You can't catch ALL from someone else.
A Risk Factor for Children
A suspected risk factor for leukemia in children is the drug Phosphocol P32. The Food and Drug Administration (FDA) has approved the drug to treat adults with fluid in the abdominal or chest cavity. But some reports have linked it to leukemia when the drug has been prescribed without FDA approval to treat children with bleeding between the joints caused by hemophilia.
Sometimes, an abnormal lymphocyte develops in a fetus. The leukemia is usually diagnosed in infancy or the first few years after birth. However, years may go by before the disease appears. Experts suggest that, in some cases, additional genetic abnormalities that occur after birth can combine to trigger ALL.
How Does ALL Develop?
ALL starts in a stem cell in the bone marrow. It can spread to other areas such as the central nervous system, the lymph nodes and, more rarely, the testes.
Stem cells form blood cells (white cells, red cells and platelets). The stem cells that become white cells start out as blast cells called lymphoblasts, which produce lymphocytes, a type of white cell.
There are three major types of lymphocytes:
- B lymphocytes, which produce antibodies to help combat infections
- T lymphocytes, which have several functions including assisting B lymphocytes to make antibodies
- natural killer (NK) cells, which can attack virus-infected cells or tumor cells
ALL develops from early-stage lymphocytes in various stages of development. Eighty-five percent of ALL cases affect B lymphocytes, and about 15 percent affect T lymphocytes. ALL rarely affects NK cells.
ALL occurs when lymphoblasts grow out of control, grow larger than normal and accumulate. These leukemic lymphoblasts don't function normally and block production of normal red cells, platelets and white cells.
Effects of Untreated ALL
If not treated, ALL can lead to:
- low numbers of red cells that can no longer supply an adequate amount of oxygen, resulting in anemia
- the immune system's inability to guard against infection effectively because of a lack of neutrophils (a type of white cell), a condition called neutropenia
- low numbers of platelets, which can cause bleeding and easy bruising with no apparent cause, a condition called thrombocytopenia