Behavior of free testosterone in patients with prostate cancer on androgen deprivation therapy

Objectives: Determination of free testosterone (FT) serum level is an efficient method to evaluate bioavailable testosterone. We analyzed the behavior of serum FT in patients with prostate cancer receiving androgen deprivation therapy (ADT) and correlated FT with total testosterone (TT). We also analyzed the efficiency of both isoforms in the evaluation of the ADT. Methods: Serum levels of TT and FT were determined in 191 patients with prostate cancer in a cross-sectional study. A subset of 56 patients submitted only to radical prostatectomy served as control group. The remaining 135 patients with advanced prostate cancer on three-month LHRH agonist treatment comprised the study group. The median age of the population was 73 years (range, 53-86 years) and the median time on ADT was 42 months (6-198). Results: A significant correlation and linear regression between TT and FT was observed (r(2) 0.948). The efficiency of TT and FT to discriminate patients with and without ADT was similar (AUC: 0.993 and 0.995, respectively, p > 0.05). A castration level of serum FT established at 1.7 pg/mL had a sensitivity of 85.9% and a specificity of 100%, which are similar to the sensitivity and specificity of 50 ng/dL of TT. All patients without ADT had levels of serum TT and FT above the castration level. In 19 of the 135 (14.1%) patients on ADT serum TT was above 50 ng/dL. In 12 of these 19 patients (63.2%) serum FT was below 1.7 pg/mL while in seven patients (5.2%) FT was also above the castration level. Conclusions: The castration level of FT was established at 1.7 pg/mL. Serum TT and TF correlated very well; however, they seemed to provide complementary information in the evaluation of ADT efficiency. 14.1% of the patients on ADT failed to reach the castration level of serum TT; determination of serum FT in these patients would reduce this rate to 5.2%.