The exact cause of leukemia has not been identified. Researchers, however, have gained a greater understanding of how specific changes in DNA can cause bone marrow stem cells to develop into leukemia.

Some forms of cancer are caused by DNA mutations that “turn on” oncogenes (genes that speed up cell division) or “turn off” tumor suppressor genes (genes that slow down cell division or cause cells to die at the right time). In people with leukemia, these mutations are normally acquired after birth. The mutations may occur from exposure to radiation or cancer-causing chemicals, but many times the mutations occur for no apparent reason.

Another DNA error that can lead to leukemia is a translocation. A translocation is the transfer of DNA from one chromosome to another. This abnormality can turn on oncogenes which causes rapid cell division.

Researchers have identified a number of factors that may make a person more likely to develop leukemia. These risk factors include:

• Exposure to high levels of radiation. Patients who have received radiation therapy as treatment for other forms of cancer have an increased risk of developing leukemia later in life. In addition, people exposed to radiation from atomic blasts (such as those in Japan during World War II) and nuclear accidents have an increased risk of developing the disease. There have been numerous studies examining the relationship of power lines to leukemia but to date, there is no definitive evidence that they cause an increased risk of cancer.
  
  
• Exposure to certain chemicals. Exposure to high levels of certain chemicals, including benzene (a chemical in gasoline and cigarette smoke) and formaldehyde, can increase a person’s risk of developing leukemia.
  
  
• Chemotherapy. Patients treated with certain chemotherapy drugs, including alkylating agents, are at an increased risk of developing leukemia later in life. The risk appears to increase with individuals who receive a higher-than-standard dose of chemotherapy drugs.
  
  
• Down syndrome and other specific genetic diseases. Patients with certain diseases caused by abnormal chromosomes, including Down syndrome, may have an increased risk of developing leukemia.
  
  
• Smoking. Cigarette smoking increases a person’s risk of developing leukemia.
  
  
• Human T-cell leukemia virus-I (HTLV-I). This virus is responsible for the development of a rare type of chronic lymphocytic leukemia.
  
  
• Myelodysplastic syndrome. This blood disease increases a person’s risk of developing acute myeloid leukemia.
  
  
• Li-Fraumeni syndrome. This condition, resulting from the inheritance of a mutation in the p53 tumor suppressor gene, may increase the risk of developing leukemia in some children.
  

Although leukemia is associated with these risk factors, many patients with the disease have no known risk factors.