A risk factor  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.
Doctors and researchers don’t know what causes most childhood cancers. A small percentage of cancers can be linked to the genetic disorder Down syndrome, other inherited genetic abnormalities , and previous radiation treatment. Environmental causes (such as exposure to infectious and toxic substances) are unlikely to cause childhood cancer.
To help doctors learn more about risk factors, the Childhood Cancer Research Network, coordinated by the Children's Oncology Group , is a North American childhood cancer registry. Once registered with the network, patients and families may be asked if doctors and researchers can contact them in the future to collect information for studies on genetic and environmental factors that may be connected to the development of childhood cancers.
Because specific causes have not been found for each individual type of childhood cancer, the way to prevent childhood cancer is still unknown.