Hyperinsulinemia and risk of lethal prostate cancer.

Abstract

e17008 Background: Epidemiologic studies have found that insulin-like growth factor (IGF)-1 causally increases prostate cancer incidence and mortality, but the effect of insulin is less clear. IGF-1 and insulin act as mitogens by binding non-selectively to their receptors. To this end, this study tests the hypothesis that high circulating insulin increases risk for lethal (fatal or metastatic) prostate cancer among men with non-metastatic prostate cancer. Methods: The study population was drawn from two U.S.-based longitudinal cohorts: the Health Professionals Follow-Up Study (HPFS) of 51,529 health professionals and the Physicians’ Health Study (PHS) of 29,067 physicians. Pre-diagnostic plasma concentration of C-peptide was used as a proxy for insulin and measured on blood collected in 1993-1995 (HPFS) or 1982 (PHS) and stratified into quartiles for analysis. The empiric lifestyle index (based on body mass index (BMI), physical activity, and diet) for hyperinsulinemia (ELIH) was calculated from questionnaire data. Covariates of interest (age and fasting status at blood draw, BMI, height, clinical stage, and tumor grade) were attained from questionnaires and medical records. We followed patients for development of metastasis or death (lethal) through 2019 (HPFS) and 2015 (PHS). SAS 9.4 and R Studio were used for analyses. Chi-squared tests and Mann Whitney U tests were used to compare differences between groups, and Cox proportional hazards models were used to estimate hazard ratios (HR) and 95% CI. Results: The sample included 2,812 men with 353 lethal prostate cancer events and a mean follow-up of 164 months from diagnosis to death. The mean time from blood draw to cancer diagnosis was 8.1 years. Compared to men with non-lethal prostate cancer, those with lethal disease had significantly more severe clinical grade and stage at diagnosis, higher BMI (25.1 vs 24.6), older age at blood draw (64.5 vs 61.9 years), and higher ELIH index. There were no differences by other covariates. There was no association between pre-diagnostic c-peptide levels and cancer-specific survival in a multivariable model that included clinical stage and grade (HR, 95% CI for high vs. low quartiles: 1.17, 0.83, 1.67). High ELIH was positively associated with risk of lethal prostate cancer (HR, 95% CI: 2.41, 1.36, 4.28), even when controlling for C-peptide (HR, 95% CI: 2.18, 1.20, 3.96). Conclusions: C-peptide levels measured prior to cancer diagnosis were not associated with increased mortality from prostate cancer. Higher ELIH was associated with increased risk of lethal prostate cancer among those diagnosed with prostate cancer, which could be partly mediated by hyperinsulinemia, but other dietary, physical activity, or BMI mechanisms could contribute.