A prospective study of the associations between treated diabetes and cancer outcomes

To quantify the association of treated diabetes with cancer incidence and cancer mortality as well as cancer case fatality and all-cause mortality in adults who subsequently develop cancer and to calculate attributable fractions due to diabetes on various cancer outcomes.

Prospective data on 599 diabetic and 17,681 nondiabetic adults from the CLUE II (Give Us a Clue to Cancer and Heart Disease) cohort in Washington County, Maryland, were analyzed. Diabetes was defined by self-reported use of diabetes medications at baseline. Cancer incidence was ascertained using county and state cancer registries. Mortality data were obtained from death certificates.

From 1989 to 2006, 116 diabetic and 2,365 nondiabetic adults developed cancer, corresponding to age-adjusted incidence of 13.25 and 10.58 per 1,000 person-years, respectively. Adjusting for age, sex, education, BMI, smoking, hypertension treatment, and high cholesterol treatment using Cox proportional hazards regression, diabetes was associated with a higher risk of incident cancer (hazard ratio 1.22 [95% CI 0.98-1.53]) and cancer mortality (1.36 [1.02-1.81]). In individuals who developed cancer, adults with diabetes had a higher risk of cancer case fatality (1.34 [1.002-1.79]) and all-cause mortality (1.61 [1.29-2.01]). For colorectal, breast, and prostate cancers, the attributable fractions resulting from diabetes were larger for cancer fatality and mortality than cancer incidence.

In this prospective cohort, diabetes appears to exert a greater influence downstream on the risk of mortality in people with cancer than on upstream risk of incident cancer.