“Given the high prevalence of obesity in our society, we felt it was critical to determine if obesity actually caused the increased incidence of leukemia and not some other associated exposure,” said Steven D. Mittelman, a pediatric endocrinologist who led the study, published in the journal Cancer Prevention Research. Mittelman is also an assistant professor of pediatrics and of physiology and biophysics at the Keck School of Medicine of the University of Southern California.
ALL is the most common form of leukemia in children, peaking in incidence at 2 to 5 years of age. In the United States, approximately 1,000 new ALL cases occur in adults each year, and another 1,000 in children. The rate of cure in children is approximately 80 percent; in adults, it’s 45 percent to 60 percent.
Mittelman’s team chose two strains of mice bred to develop ALL. They randomly divided each of them into two groups—a normal-diet control group and a high-fat diet group. The experiment showed that obesity itself increased the risk of ALL in both strains, especially in older mice. These findings jibed with the pattern in other exposure-related cancers, in which the deleterious effects of exposure to an irritant build up over time, as in lung cancer (smoke) and breast cancer (estrogen). Obesity’s effect on older mice also was consistent with the other fatness-related effects from cumulative exposure such as heart disease, diabetes, and arthritis.
“Our findings are consistent with epidemiological data that show a higher incidence of leukemia in obese adults and suggests that these observations are actually due to obesity, and not some associated genetic, socioeconomic, or lifestyle factor,” said Mittelman.
“These data imply that some hormone or factor in overweight individuals, perhaps produced by fat tissue itself, may signal leukemia cells to grow and divide. Since leukemia is the most common type of childhood cancer, understanding how obesity may increase its incidence could have important public health implications.”