Kiyabu GY, et al. - Researchers aimed at ascertaining the association between plasma C-peptide concentration and prostate cancer. They matched 201 prostate cancer cases and 402 controls by age, public health center area, residence, date and time of blood collection, and fasting duration before blood collection using the Japan Public Health Center-based Prospective study. Median plasma C-peptide concentration overall was not identified to have a significant association with prostate cancer. However, stratification of prostate cancer by stage suggested that the association between plasma C-peptide concentration and prostate cancer risk varied by cancer stage. Hence indicating the significance of differentiation of localized and advanced prostate cancer cases when investigating the association between plasma C-peptide concentration and the risk of prostate cancer.