Measurement of testosterone levels during androgen deprivation therapy (ADT) is broadly recommended, but how therapy should be altered in response to testosterone values during ADT remains controversial. Our objective was therefore to evaluate the relation between testosterone and concomitant prostate specific antigen (PSA) levels during ADT on clinical outcomes.

Patients from the continuous androgen deprivation (CAD) arm of the PR.7 trial of intermittent ADT for biochemically recurrent prostate cancer following radiotherapy were included. Statistical analyses evaluated the prognostic importance of testosterone levels during ADT relative to concomitant PSA levels. We similarly evaluated whether the number of testosterone breakthroughs >1.7nmol/L predicted the time to castrate-resistant prostate cancer (CRPC), cancer specific survival (CSS) or overall survival (OS) with Kaplan-Meier and Cox-regression analyses.

Overall, the prognostic importance of testosterone on outcomes was eclipsed by the prognostic value of concomitant PSA values. The occurrence of testosterone values >0.7nmol/L in the first year of therapy was associated with subsequent rises >1.7nmol/L but the number of testosterone breakthroughs per patient had no relationship to the risk of CRPC, CSS or OS. A time-dependent adjusted analysis indicated as expected that PSA values were prognostic, but there was no association of relative cumulative testosterone exposure with outcomes.

In this large-scale trial with long follow up, breakthrough testosterone was unrelated to time to CRPC, CSS, or OS. Castrate testosterone values during ADT for recurrent prostate cancer provides prognostic information which must be considered alongside the time since ADT initiation and concomitant PSA values.