Researchers from the M. D. Anderson Cancer Center have reported that obesity and weight gain increase the risk of developing chronic myeloid leukemia (CML). The details of this case-control study were published in the May, 2009 issue of Cancer Epidemiology Biomarkers and Prevention.[1]

Chronic myeloid leukemia (CML) is the abnormal growth of relatively mature myeloid cells. The disease is associated with a chromosomal abnormality, where genetic material from chromosome 9 is transferred to chromosome 22. This forms what is called the Philadelphia chromosome, which plays a role in the development of the disease. This translocation results in the fusion of two proteins, BCR and ABL, which confers a selective advantage to the growth of CML cells over normal cells. The cause of this translocation is unknown.

CML occurs in males more often than in females and in Caucasians more often than in African Americans. Because the average age at diagnosis is older than 67 years, it is suspected that unknown environmental exposure over a long period of time is required to cause CML. There are no clear hereditary factors associated with CML. Identical twins of patients with CML are at no greater risk of developing CML than other siblings. One study has found that a specific HLA type, DR4, is associated with a lower incidence of CML, however, researchers have not yet identified the reason for this decrease. There is some evidence that exposure to agricultural chemicals and radiation exposure may increase the risk of developing CML. Thus, the major causes of CML remain unknown, making it impossible to institute preventative measures.

Obesity has been linked to increased risks for developing ovarian cancer, hormone positive breast cancer, endometrial cancer, high-risk prostate cancer, pancreatic cancer, thyroid cancer, esophageal cancer, gall bladder cancer, and colon cancer. However, with the exception of multiple myeloma, no hematologic malignancies have made this list.

Researchers involved in the current study compared obesity parameters of 253 patients with CML with those of 270 matched controls. They made the following observations:

• CML patients and controls had similar exposure to alcohol, tobacco, occupational solvents, and ionizing radiation.
• 11% of CML patients had occupational exposure to agricultural chemicals versus 3% of controls.
• CML patients were four times more likely to be obese during adulthood than controls.
• CML patients were five times more likely to be obese at age of diagnosis compared with controls.
• Obesity at all ages was an independent risk factor for developing CML.
• Persons who gained >1kg/year between the ages of 25 and 40 were 3.6 times more likely to develop CML.

These authors stated: “Our results suggest that obesity and adulthood weight gain play important roles in CML risk.”

Comments: This is the first study to suggest that changing lifestyle may affect the incidence of CML.

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