Introduction

Lower nadir serum testosterone (T) levels in prostate cancer (PCa) patients receiving continuous androgen deprivation therapy (ADT) has been shown to be associated with improved cancer-specific survival and time to hormone resistance. In light of recommendations for measuring T level and acting on its result, we set out to determine whether variations in serum T levels exist among patients with ideal testosterone castration response.

Methods

Serum T levels were obtained retrospectively from a random sample of 551 PCa patients receiving continuous ADT between 2007 and 2016, accounting for a total of 4,815 measurements. All patients achieved T levels ≤0.7 ng/mL during course of treatment (i.e. ideal T responders), and all T levels recorded were obtained subsequent to achieving a T level ≤0.7 ng/mL. Serum T levels were measured using a chemiluminescent microparticle immunoassay (Abbott Diagnostics® ARCHITECT i2000). Statistical significance was set at p=0.05. Analysis was performed using SPSS v23.0.

Results

Mean patient age was 73.7 years. Mean T level was 0.52 ng/mL (std dev=0.34 ng/mL). There was no significant association between patient age and T levels (p= .07). Serum T levels did not demonstrate any diurnal variation, as there was no association between time of day that blood samples were drawn and T levels (p= .14). After attaining T levels ≤0.7 ng/mL, 237 (43.0%), 127 (23.0%), and 25 (4.5%) patients subsequently achieved T levels >0.7, >1.1 and >1.7 ng/mL, respectively, with 85% of patients who had a T level >0.7 ng/mL having at least one additional T level measurement >0.7 ng/ml within 5 years. Ideal T levels of ≤0.7 ng/mL were re-achieved in 185 (78.1%), 84 (66.1%) and 15 (60.0%) of patients who had T levels measurements of >0.7, >1.1, and 1.7 ng/ml, respectively.

Conclusions

Ideal T responders to continuous ADT demonstrate considerable variation in serum T levels on follow up. Elevated T level measurements among patients on continuous ADT must be interpreted in light of these findings. Repeat T level measurements are recommended prior to implementing a change in clinical management.

Funding

None