title: Association of C-peptide and leptin with prostate cancer incidence in the Health Professionals Follow-up Study.
abstract: OBJECTIVE
  Hyperinsulinemia is hypothesized to influence prostate cancer risk. Thus, we evaluated the association of circulating C-peptide, which is a marker of insulin secretion, and leptin, which is secreted in response to insulin and influences insulin sensitivity, with prostate cancer risk.
  
  
  METHODS
  We identified prostate cancer cases (n = 1,314) diagnosed a mean of 5.4 years after blood draw and matched controls (n = 1,314) in the Health Professionals Follow-up Study. Plasma C-peptide and leptin concentrations were measured by ELISA. Odds ratios (ORs) and 95 % confidence intervals (CI) were estimated taking into account the matching factors age and history of a PSA test before blood draw and further adjusting for body mass index, diabetes, and other factors.
  
  
  RESULTS
  Neither C-peptide (quartile [Q]4 vs. Q1: OR 1.05, 95 % CI 0.82-1.34, p-trend = 0.95) nor leptin (Q4 vs. Q1: OR 0.85, 95 % CI 0.65-1.12, p-trend = 0.14) was associated with prostate cancer risk. Further, neither was associated with risk of advanced or lethal disease (n = 156 cases; C-peptide: Q4 vs. Q1, OR 1.18, 95 % CI 0.69-2.03, p-trend = 0.78; leptin: Q4 vs. Q1, OR 0.74, 95 % CI 0.41-1.36, p-trend = 0.34).
  
  
  CONCLUSIONS
  In this large prospective study, circulating C-peptide and leptin concentrations were not clearly associated with risk of prostate cancer overall or aggressive disease. Well into the PSA era, our findings do not appear to be supportive of the hypothesis that hyperinsulinemia influences risk of total or aggressive prostate cancer.
authors.affiliation: Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Rm E6132, 615 N. Wolfe Street, Baltimore, MD, 21205, USA.
authors.forename: Gabriel Y
authors.initials: GY
authors.lastname: Lai
authors.forename: Edward L
authors.initials: EL
authors.lastname: Giovannucci
authors.forename: Michael N
authors.initials: MN
authors.lastname: Pollak
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Peskoe
authors.forename: Meir J
authors.initials: MJ
authors.lastname: Stampfer
authors.forename: Walter C
authors.initials: WC
authors.lastname: Willett
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Platz
mesh_terms: D000368:Aged; D002096:C-Peptide / Q000097:blood*; D016022:Case-Control Studies; D048708:Cell Growth Processes / Q000502:physiology; D015331:Cohort Studies; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D020738:Leptin / Q000097:blood*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011471:Prostatic Neoplasms / Q000097:blood*; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D002096:C-Peptide; D020738:Leptin