Risk Factors

Almost all cases of CML have no identifiable predisposing factors, and even when there might be a plausible causal link, it is extremely difficult to incriminate any factor in individual patients. Exposure to ionizing radiation is the only known etiological factor; the incidence of CML was increased to a minor but significant degree in patients treated with radiation therapy for ankylosing spondylitis or metropathia hemorrhag-ica.1011 The most compelling link between radiation exposure and CML comes from a [Life Span] study of survivors of the atomic bomb explosions in Hiroshima and Nagasaki (Japan) in 1945.12 13 There was an increased risk of CML among the survivors. An increased risk of leukemia, but not of CML, has also been reported in an area immediately surrounding the British nuclear fuel facility at Calder Hall in Cumbria, U.K. (although a government commission of enquiry was unable to confirm this).

There are no firm associations of exposure to toxic chemicals or any infectious agent and CML.

Chemicals that damage the bone marrow, in particular aromatic hydrocarbons and benzene, appear to predispose to acute myeloid leukemia (AML), but it is impossible to be certain that leukemia would not have developed in a particular patient in the absence of exposure to the suspect substance. Recently, it has been shown that benzene activates an oncogene that causes AML.

Though a small number of families with a high incidence of CML have been reported, there is no confirmed familial predisposition and no definite association with human leukocyte antigen (HLA) genotypes and CML.14 Interestingly, two HLA types are associated with a decreased incidence of CML.15 Relapse of CML originating in donor cells following related allogeneic stem cell transplantation has been recorded.16 It is also noteworthy that only rarely does the identical twin brother or sister of a person with CML also develop leukemia. In a study of 40 pairs of identical twins in which one twin had CML, there was no instance in which the other twin developed CML.

Unlike the case in certain common epithelial cancers, there are no known dietary or social habits that increase the risk of acquiring CML. Smoking cigarettes has been weakly implicated. This link is dependent on the duration of exposure and the age of starting to smoke.

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