B89

Objective: A recent meta-analysis reported that numerous studies have generally observed a decreased risk in prostate cancer among diabetics. However, other studies have reported both positive and inverse associations between the metabolic syndrome and prostate cancer risk. The objective of this study was to evaluate the association of C-peptide, a marker of insulin secretion, with subsequent diagnosis of prostate cancer.
 >Methods: Histologically confirmed prostate cancer cases (n = 264) and matched controls (n = 264) were identified between baseline in 1989 and December 2002 in the CLUE II cohort of Washington County, Maryland. Cases were ascertained via linkage to the Washington County Cancer Registry and, since 1992, to the Maryland Cancer Registry, from which stage and Gleason sum at diagnosis were obtained. Controls were matched to cases on age at blood donation, race, date of blood draw, and the number of hours between the last meal and blood draw. Concentrations of C-peptide were measured in baseline blood specimens using an enzyme-linked immunosorbent assay. Body mass index (BMI) at baseline and age 21, use of diabetes medication, dietary factors, and use of vitamin supplements were self-reported at baseline. Odds ratios (ORs) and 95% confidence intervals (CI) were estimated from conditional logistic regression models. We assessed confounding and present a parsimonious model.
 >Results: Median concentration of C-peptide were statistically significantly lower in cases (1180.1 pmol/L) compared with controls (1365.4 pmol/L; p = 0.009). Compared with the bottom fourth, the highest fourth of plasma C-peptide concentration was inversely associated with prostate cancer risk (OR = 0.65, 95% CI = 0.37 - 1.14; ptrend = 0.08), especially organ-confined disease (OR = 0.44, 95% CI = 0.19 - 0.97; ptrend = 0.04), after adjusting for overweight or obesity status and family history of prostate cancer. The associations remained similar when the analysis was restricted to participants without diabetes or when cases diagnosed during the first five years of follow-up were excluded. BMI did not modify the association between C-peptide and prostate cancer overall or organ-confined disease.
 >Conclusions: Like diabetes and, in some studies, the metabolic syndrome, concentration of C-peptide appeared to be inversely associated with subsequent diagnosis of prostate cancer, especially organ-confined cases.
 >Funding: EDRN U01 CA 86308; Cancer Epidemiology, Prevention, and Control Training Fellowship (T32 CA 009314)

Sixth AACR International Conference on Frontiers in Cancer Prevention Research-- Dec 5-8, 2007; Philadelphia, PA