All blood cancers are caused by changes (mutations) in DNA within blood cells. This causes the blood cells to start behaving abnormally. In almost all cases, these changes are linked to things we can't control. They happen during a person's lifetime, so they are not genetic faults you can pass down to children.
Although we don’t normally know exactly why someone has developed leukemia blood cancer, there are things that we know can affect your risk:
radiation or chemical exposure
some health conditions and treatments
How these affect factors risk depends on the type of blood cancer.