Matching-Adjusted Indirect Comparison of the Efficacy of Apalutamide and Enzalutamide with ADT in the Treatment of Non-Metastatic Castration-Resistant Prostate Cancer

Introduction: Apalutamide and enzalutamide are next-generation androgen receptor inhibitors that demonstrated efficacy in placebo-controlled studies (SPARTAN for apalutamide; PROSPER for enzalutamide) when used in combination with androgen deprivation therapy (ADT) for treatment of non-metastatic castration-resistant prostate cancer (nmCRPC). In the absence of comparative studies between these agents, the present study sought to indirectly compare metastasis-free survival (MFS) and overall survival (OS) in patients with nmCRPC who received these therapies.

Methods: Individual patient-level data from SPARTAN (apalutamide plus ADT) and published data from PROSPER (enzalutamide plus ADT) were utilized. An anchored matching-adjusted indirect comparison (MAIC) was conducted by weighting the patients from the SPARTAN study to match baseline characteristics reported for PROSPER. Hazard ratios (HRs) for MFS and OS were re-estimated for SPARTAN using weighted Cox proportional hazards models and indirectly compared with those of PROSPER using a Bayesian network meta-analysis.

Results: From the SPARTAN population (N = 1207), a total of 1171 patients were matched to the PROSPER population (N = 1401). The recalculated HRs (95% confidence interval) for apalutamide versus ADT based on the reweighted SPARTAN data to mimic the PROSPER patient population were 0.26 (0.21; 0.33) for MFS and 0.62 (0.41; 0.94) for OS. MAIC-based HRs (95% credible interval) for apalutamide versus enzalutamide were 0.91 (0.68; 1.22) for MFS and 0.77 (0.46; 1.30) for OS. The Bayesian probabilities of apalutamide being more effective than enzalutamide were 73.6% for MFS and 83.5% for OS.

Conclusions: MAIC results suggest that nmCRPC patients treated with apalutamide have a higher probability of a more favorable MFS and OS compared with those treated with enzalutamide.