Postmenopausal women with treated diabetes may be at an increased risk for lung cancer, particularly if they are on insulin, say researchers.
"To our knowledge, this is the first prospective study to examine whether the risk for lung cancer incidence is associated with diabetes treatments or duration," say Juhua Luo (West Virginia University, Morgantown, USA) and colleagues.
Preclinical studies support a role for diabetes in lung cancer development but epidemiologic evidence on the association of diabetes with lung cancer is limited and conflicting, says the team. "The primary barrier to a more clear understanding of the association has been the lack of prospective studies of sufficient size and duration."
The researchers therefore decided to assess associations between diabetes, diabetes therapy, and lung cancer risk in participants from The Women's Health Initiative, a large prospective study of 145,765 postmenopausal women in which detailed information on diabetes and potential risk factors was collected at baseline.
The cohort included 8154 individuals with diabetes at enrollment and participants were followed for a mean of 11 years, with 2257 cases of lung cancer diagnosed.
Information on diabetes drug therapy was collected using participants' self-reported history at baseline and a face-to-face review of their medication which they took with them to the baseline visit.
As reported in Diabetes Care, the researchers found that women with diabetes were not at an increased risk for lung cancer compared with those who did not have diabetes at baseline, after adjustment for potential confounders.
However, women who were taking treatment for their diabetes were at a significant 27% greater risk for lung cancer than nondiabetic women.
On dividing the diabetic women by treatment type according to the baseline medication review, the team found that women with diabetes requiring insulin treatment were 71% more likely to develop lung cancer, compared with women without diabetes.
The team also reports that there was no significant association between duration of diabetes and lung cancer risk.
"Studies have shown that elevated insulin potentiates the activity of insulin-like growth factor 1 (IGF-1)… which can lead to a higher risk for lung cancer," say Luo et al. "A hospital-based case-control study also detected a dose-dependent association between plasma IGF-1 levels and lung cancer," they add.
"More large prospective studies are needed to examine whether the increased risk of lung cancer among women with treated diabetes is driven by specific types of oral diabetes drugs, exogenous insulin treatment, high endogenous insulin levels, poor glycemic control, or longer diabetes severity," concludes the team.
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