The disease can occur in adults (usually middle-aged) and children. CML affects 1 to 2 people per 100,000 and accounts for 7% to 20% cases of leukemia. It is usually associated with a chromosome abnormality called the Philadelphia chromosome. Exposure to ionizing radiation is one possible trigger for this chromosome abnormality. Such exposure could occur from a nuclear disaster or from treatment of a previous cancer, like thyroid cancer or Hodgkin's lymphoma. However, the vast majority of people treated for cancer with radiation do not go on to develop leukemia. It takes many years to develop leukemia from this cause.
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