OBJECTIVE:

Diabetes is associated with many forms of cancer. Recent evidence has suggested that some treatments for diabetes are associated with an increased cancer risk. Less is known about the association between endogenous insulin in the prediabetes state and cancer risk.

RESEARCH DESIGN AND METHODS:

We investigated cumulative cancer incidence and cancer incidence density over 29 years, according to basal insulin, in a cohort of 1,695 nondiabetic men and women of four ethnic origins, aged 51.8 ± 8.0 years at baseline. Total mortality among the 317 subjects (18.7%) who developed cancer at least 2 years after baseline was assessed.

RESULTS:

In a Cox proportional hazards model, the all-site hazard ratio of cancer incidence comparing the highest insulin quartile with the other three quartiles was 1.09 (95% CI 0.85-1.40), adjusted for age, sex, and ethnicity. BMI, smoking, and fasting blood glucose were not statistically significant in this model. Basal insulin level was not significantly associated with cancer of specific sites (breast, prostate, colon/rectum, or bladder). Fasting insulin in the upper quartile conferred a 37% increased risk for total mortality among cancer patients, adjusting for age, sex, and ethnic origin (95% CI 0.94-2.00, P = 0.097) compared with that of the lower quartiles. Male sex, older age, and North African origins were associated with a greater risk of mortality during follow-up time.

CONCLUSIONS:

This long-term cohort study may suggest a role for basal elevated insulin levels, mainly as a negative predictor in cancer prognosis.