Selenium (Se) is essentially needed for the biosynthesis of selenoproteins. Low 
Se intake causes reduced selenoprotein biosynthesis and constitutes a risk 
factor for tumorigenesis. Accordingly, some Se supplementation trials have 
proven effective to reduce prostate cancer risk, especially in poorly supplied 
individuals. Because Se metabolism is controlled by selenoprotein P (SEPP), we 
have tested whether circulating SEPP concentrations correlate to prostate cancer 
stage and grade. A total of 190 men with prostate cancer (n = 90) and "no 
evidence of malignancy" (NEM; n = 100) histologically confirmed by prostate 
biopsy were retrospectively analyzed for established tumor markers and for their 
Se and SEPP status. Prostate specific antigen (PSA), free PSA, total Se, and 
SEPP concentrations were determined from serum samples and compared with 
clinicopathologic parameters. The diagnostic performance was analyzed with 
receiver operating characteristic curves. Median Se and SEPP concentrations 
differed significantly (P < 0.001) between the groups. Median serum Se 
concentrations in the 25th to 75th percentile were 95.9 microg/L (82-117.9) in 
NEM patients and 81.4 microg/L (67.9-98.4) in prostate cancer patients. 
Corresponding serum SEPP concentrations were 3.4 mg/L (1.9-5.6) in NEM and 2.9 
mg/L (1.1-5.5) in prostate cancer patients. The area under the curve (AUC) of a 
marker combination with age, PSA, and percent free PSA (%fPSA) in combination 
with the SEPP concentration, yielded the highest diagnostic value (AUC 0.80) 
compared with the marker combination without SEPP (AUC 0.77) or %fPSA (AUC 
0.76). We conclude that decreased SEPP concentration in serum might represent an 
additional valuable marker for prostate cancer diagnostics.