Childhood cancers most often begin in the stem cells, which are the basic cells capable of producing more specialized cells. If these cells undergo a change or mutation, the result is some form of cancer.

Many types of childhood cancers appear very early in life without any apparent cause.  Unlike cancers of the adults, childhood cancers are not significantly related to lifestyle risk factors, such as tobacco use but environmental exposures have not been ruled out.

Family history and genetics may play an important role in childhood cancers. Varying forms of the same cancer may appear more than once in a family. However, in these cases, it is unknown whether the cancer is caused by genetic factors or environmental elements, such as exposure to chemicals near the family’s residence or toxins in the diet. Some scientists believe cancer could result from a combination of these factors.

Other proposed associations with childhood cancers include:

• Viruses. Certain viruses, such as the Epstein–Barr virus (EBV) and the human immunodeficiency virus (HIV), have been linked to an increased risk in developing specific childhood cancers. These cancers include Hodgkin’s and non-Hodgkin’s lymphoma. Scientists believe that the virus alters the cell until it becomes a cancer cell. Some researchers are studying associations between certain infections as triggers for childhood cancers. Recent research has also shown increased rates of childhood leukemias occurring after influenza outbreaks in Great Britain.
  
  
• Environmental agents. Pesticides, fertilizers, and power lines have been investigated as potential links to childhood cancers. There has been evidence of cancer occurring among non-related children in certain neighborhoods, schools or cities. It is unknown whether prenatal or infant exposure to these agents causes childhood cancers. Some researchers believe it is merely a coincidence rather than a direct cause and effect. A cause and effect relationship of exposure to power lines has not been established.
  
  
• Cancer treatments. High-dose radiation therapy and chemotherapy have been linked to childhood cancers. Children who have been exposed to this type of treatment may have an increased risk of developing a second malignancy later in life. Scientists believe that strong anti-cancer agents may alter the cells and possibly the immune system.

There are many theories as to possible risk factors and causes for cancers in children. However, the cause for most childhood cancers is unknown.