ORLANDO, FL USA (UroToday.com) - Dr. Lucas Regis presented an institutional series on whether free serum testosterone (FT) or total testosterone (TT) can be a surrogate marker for the clinical benefit of androgen suppression in prostate cancer patients. The mean follow up for their study was 107 months (range: 22-304 months). A total of 36 patients (49.3%) developed castration resistance (CR), 15 patients (20.5%) developed metastatic spread, and 6 patients (9.2%) died of disease. From 73 patients who were on LHRH agonist for at least 12 months, they obtained TT (chemiluminescent assay-lower sensitivity 10 nd/dL) and FT (analogue ligand radioimmunoassay-lower sensitivity 0.05 pg/mL). In order to establish the castration level of FT with clinical impact, survival analysis using 50, 32 and 20 ng/dL for TT, and 1.7, 1.1 and 0.7 pg/mL for FT was performed.
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On multivariable analysis, FT (OR=4.33, p <0.001) and Gleason score (OR=2.73, p < 0.005) were the two independent predictors of survival, independent of CR. Dr. Regis reported that any TT threshold demonstrated significant differences for survival. In comparison, FT of 1.1 pg/mL was the lower threshold and showed significant differences in survival free of CR. The active form of testosterone (FT) represents 2% of TT while 40% is bound to SHBG and 58% to albumin.
In this study, authors show that in comparison to TT, FT is a better surrogate marker of CR in patients who are receiving LHRH agonist.
Presented by Lucas Regis at the American Urological Association (AUA) Annual Meeting - May 16 - 21, 2014 - Orlando, Florida USA
Written by Reza Mehrazin, MD, medical writer for UroToday.com