Factors Predicting the Off-treatment Duration in Patients with Prostate Cancer Receiving Degarelix as Intermittent Androgen Deprivation Therapy

Abstract

BackgroundIntermittent androgen deprivation therapy (IAD) is commonly used in prostate cancer because of the benefits of the off-treatment period (OTP). The off-treatment time for patients depends on cancer progression, often measured as a rise in prostate-specific antigen (PSA). ObjectiveTo evaluate if certain factors can predict OTP duration following 7-mo degarelix therapy. Design, setting, and participantsThis multivariable analysis included 191 prostate cancer patients with baseline PSA 4–50 ng/ml or PSA doubling time <24 mo entering the first OTP with PSA ≤4 ng/ml and testosterone <0.5 ng/ml. OTP continued until disease progression, measured as PSA >4 ng/ml. Despite a study-defined OTP maximum of 24 mo, a 50% failure rate was not observed within certain strata. A Weibull distribution was used to estimate median time to PSA >4 ng/ml adjusted for the following variables: age; baseline (or end of induction period [EOI]) PSA; baseline testosterone; cancer stage/previous curative treatment; and Gleason score. According to the results and the utility of these factors in clinical practice, the model was reduced in a stepwise manner. Time to testosterone recovery (testosterone >0.5 and >2.2 ng/ml) was estimated in a similar manner. ResultsThe full five-factor model showed that baseline PSA (p<0.0001), age (p=0.004), prostate cancer stage/previous therapy (p=0.023), and baseline testosterone (p=0.039) influenced OTP. A reduced two-factor model (baseline PSA, age) showed that only baseline PSA influenced OTP (p<0.0001), and patients with baseline PSA ≤4 ng/ml had the longest OTP. In addition, EOI PSA (p<0.0001) and age (p=0.050) significantly influenced OTP. The times to testosterone >0.5 and >2.2 ng/ml were longer for older patients and those with lower baseline testosterone levels. ConclusionPatients with lower baseline and EOI PSA, and older patients can stay off therapy longer and therefore may benefit more from degarelix IAD. These factors may help in proposing an algorithm to predict the OTP and optimise visit frequency. Patient summaryWe describe extended analysis results for a trial in which patients with prostate cancer received intermittent androgen deprivation treatment. Prostate-specific antigen levels at baseline and at the end of the induction period, as well as older age, predicted the duration of the off-treatment period. Testosterone recovery was slower in older patients and in patients who had lower pretreatment testosterone levels. These factors may help in deciding whether to choose continuous or intermittent treatment as a strategy. Trial registrationClinicaltrials.gov NCT00801242