Observational studies on selenium and risk of advanced prostate cancer (1) listed by mean or median selenium concentrations. ORs and 95% CIs were obtained in a comparison of the highest with the lowest quantile of seleniuim. ▲, nested case-control study (CCS) and case cohort study with selenium concentrations obtained from serum or plasma; ●, population-based CCS with selenium concentrations obtained from serum or plasma; △, nested CCS and case cohort study with selenium concentrations obtained from toenails; ○, population-based CCS with selenium concentrations obtained from toenails. Observational studies were excluded if they used a questionnaire-based assessment of selenium intake, included patients with benign prostatic hyperplasia as controls, or included < 15 prostate cancer cases. Advanced cancer was defined as a tumor that extends through the prostatic capsule or as a metastatic disease (stage C or D, stage III or IV, or regional or distant stage); the exception was Vogt et al (55), who defined advanced cancer as regional or distant stage, Gleason Score ≥ 7, or both.