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. 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 CML is not known, though researchers now understand how the disease develops from genetic changes in the myeloid cells. Environmental factors account for only a small number of CML diagnoses, and family history does not appear to play a role in the development of CML.
The following factors may raise a person's risk of developing CML:
Age. The average age of a person with CML is around 60. CML is uncommon in children and adolescents.
Radiation exposure. There was an increase in the rate of CML in Japan in long-term survivors of the 1945 atomic bombings. However, there is no proven link between CML and radiation therapy or chemotherapy given for other types of cancer or other diseases.
Gender. Men have a somewhat higher risk of CML than women.