A risk factor [2] is anything that increases a person's chance of developing cancer. Although risk factors often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.

The cause of ALL is not known. In general, ALL is most likely to affect children and older adults. The following factors may raise a person's risk of developing ALL:

Age. Children younger than 15 and adults older than 50 are more likely to develop ALL.

Race. White people are somewhat more likely than black people to develop ALL for reasons that are not understood.

Genetic disorders. People with Down syndrome, ataxia telangiectasia [3], Li-Fraumeni syndrome [4], Klinefelter syndrome, Fanconi anemia, Wiskott-Aldrich syndrome, and Bloom syndrome are at higher risk for ALL than the general population.

High doses of radiation. People who have been exposed to high levels of radiation, such as long-term survivors of atomic bombs, may be more likely to develop ALL. Exposure to electromagnetic fields or high-voltage electric lines has not been proven to increase a person's risk of ALL.

Viruses. Occasionally, ALL or unique types of lymphoma can be associated with a previous viral infection, such as human T-cell leukemia virus-1 or Epstein-Barr virus.

Recent genetic research has shown that many young children who develop ALL may have had the disease before they were born, although it may take several years before the disease develops and causes symptoms. More research is being done to try to understand this finding in more detail.