Factors predicting progression to castrate-resistant prostate cancer in patients with advanced prostate cancer receiving long-term androgen-deprivation therapy

Abstract

Objectives: To assess time to progression to castrate-resistant prostate cancer (CRPC) and factors influencing longer-term outcomes in patients receiving androgen-deprivation therapy (ADT) in an extension to the Triptocare study (NCT01020448). This is pertinent as the Triptocare study did not show that urinary prostate cancer antigen-3 (PCA3) score was a reliable marker of cancer stage in advanced prostate cancer and was not useful for assessing response 6 months after initiation of ADT with triptorelin 22.5 mg. Patients and Methods: An international, multicentre, non-interventional, observational, longitudinal, prospective study involving patients from the Triptocare study. CRPC status of patients was collected for up to 3 years from ADT initiation. Patient treatment and assessments were at the investigator's discretion. Co-primary endpoints were rate of CRPC at 3 years after initiating ADT and the median time to CRPC. An exploratory endpoint was the association of Triptocare baseline variables (including TMPRSS2-ERG and PCA3 scores) and PCA3 score at Triptocare last value available with CRPC onset. Results: Of the 325 patients in the Triptocare study safety population, 180 patients were enrolled in the Triptocare LT study (102 received continuous and 78 received intermittent ADT). CRPC rates at 3 years were 24/102 (23.5%) and 6/78 (7.7%) patients in the continuous and intermittent ADT groups, respectively. The median time to CRPC was not reached for either group. PCA3 score status at baseline was the only variable associated with a higher risk of progression to CRPC in both the intermittent and continuous ADT groups; compared with a baseline PCA3 score of ≥35, a PCA3 score below the level of quantification had a hazard ratio (HR) of 20.04 ([95% confidence interval (CI) 2.71–148.34] and a HR of 9.44 [95% CI 2.39–37.27], respectively). Baseline metastatic disease and testosterone level were additionally associated with progression to CRPC in the continuous ADT population (HR 5.20, 95% CI 1.68–16.06 and HR 0.995, 95% CI 0.991–0.999, respectively). Conclusion: In men with locally advanced or metastatic prostate cancer, a PCA3 score of ≥35 at the time of initiating ADT may predict a lower risk of developing CRPC in the following 3 years.