Having a risk factor for a disease statistically influences your chance of getting that disease. For example, smoking is a risk factor for lung cancer, as well as a number of other diseases. But not everyone who is at risk for a particular disease will get the disease. And many people who do get it may have no known risk factors.
Chronic myeloid leukemia (CML) is caused by a mutation. But no one understands why this happens. There are a few factors that may increase the risk of CML. But for most people with CML, there's no known cause.
The only known environmental risk factor for CML is the exposure to high-dose radiation, which is rare. (Survivors of a nuclear reactor accident, for example.) But there's no proven connection between CML and the therapeutic radiation given for other diseases.
Age and gender
The risk of getting CML increases with age. This disease is slightly more common in males than females, but it's not known why.
There are no other established risk factors for CML. The risk of getting CML does not seem to be affected by smoking, diet, exposure to chemicals, or infections. And CML does not run in families.