Oncology · Medical Literature
Exploratory Time-Dependent Patterns in Estimated Treatment Effect of Talazoparib Plus Enzalutamide in HRR Non-Deficient or Unknown Metastatic Castration-Resistant Prostate Cancer: A Post Hoc Analysis of the TALAPRO-2 Trial.
Abstract
Talazoparib plus enzalutamide improved overall survival (OS) in the biomarker-unselected TALAPRO-2 population, but OS benefit was not statistically significant in the homologous recombination repair (HRR) non-deficient or unknown subgroup, whereas radiographic progression-free survival (rPFS) was prolonged. We explored time-dependent patterns in estimated treatment effects in this subgroup. Approximate individual-level data for 636 patients were reconstructed from published Kaplan-Meier curves; original trial-level patient data were unavailable. The proportional hazards assumption was assessed using Schoenfeld residuals and log-log plots. Interval-specific hazard ratios (HRs) were estimated using piecewise Cox models. A treatment-by-log(time + 1) interaction was evaluated formally. Sensitivity analyses included alternative interval schemes, landmark analyses, restricted mean survival time (RMST), and descriptive application of the same piecewise framework to the HRR-deficient subgroup. The proportional hazards assumption was not rejected for OS (p = 0.63) or rPFS (p = 0.37). For OS, the 36-48-month interval showed a nominally lower hazard with talazoparib (HR 0.59; 95% confidence interval [CI] 0.36-0.97; nominal p = 0.039). For rPFS, the lowest HR occurred at 0-6 months (HR 0.56; 95% CI 0.37-0.86; p = 0.008). Treatment-by-log(time + 1) interactions were not statistically significant for OS (p = 0.44) or rPFS (p = 0.12). This reconstructed-data post hoc analysis suggested exploratory time-dependent patterns in effect estimates without formal evidence of a time-varying treatment effect. Findings are descriptive, hypothesis-generating, and should not be extrapolated to molecularly confirmed HRR-proficient disease. ClinicalTrials.gov: NCT03395197.
Clinical relevance
This post hoc analysis of the TALAPRO-2 trial addresses a clinically important subgroup — patients with HRR non-deficient or unknown metastatic castration-resistant prostate cancer (mCRPC) — in whom the OS benefit of talazoparib plus enzalutamide did not reach statistical significance despite improved rPFS, leaving clinicians uncertain about the magnitude and timing of benefit in this population. Understanding the temporal pattern of treatment effects is critical for patient counseling, treatment sequencing, and trial design in biomarker-unselected mCRPC. This analysis is particularly timely as PARP inhibitor combinations become more widely adopted in HRR-unselected populations following regulatory approvals.
Key findings
1. The proportional hazards assumption was not formally rejected for either OS (Schoenfeld residuals p = 0.63) or rPFS (p = 0.37), indicating no statistically significant time-varying treatment effect in this subgroup. 2. A piecewise Cox model identified a nominally significant OS benefit in the 36–48-month interval favoring talazoparib plus enzalutamide (HR 0.59; 95% CI 0.36–0.97; nominal p = 0.039), though this was exploratory and not corrected for multiplicity. 3. For rPFS, the largest treatment benefit was observed in the earliest interval (0–6 months), with HR 0.56 (95% CI 0.37–0.86; p = 0.008), suggesting early radiographic disease control in the HRR non-deficient or unknown subgroup. 4. Formal treatment-by-log(time + 1) interaction tests were non-significant for both OS (p = 0.44) and rPFS (p = 0.12), confirming the absence of statistically robust time-varying treatment effect modification. 5. The analysis was conducted on reconstructed approximate individual-level data for 636 patients derived from published Kaplan-Meier curves, as original trial-level patient data were unavailable — a key methodological limitation affecting precision of all estimates. 6. Sensitivity analyses (alternative interval schemes, landmark analyses, RMST, and descriptive application to the HRR-deficient subgroup) were performed to contextualize findings, but all results remain descriptive and hypothesis-generating.
Practice implications
Clinicians should not extrapolate these exploratory findings to guide treatment decisions in patients with molecularly confirmed HRR-proficient mCRPC, as the OS benefit of talazoparib plus enzalutamide in this subgroup remains statistically non-significant and all interval-specific findings are hypothesis-generating only. The early rPFS signal (HR 0.56 at 0–6 months) may inform patient counseling regarding the timing of radiographic benefit, but should not alter current biomarker-driven patient selection until confirmed in prospective studies with pre-specified subgroup analyses. Future trials in this space should prospectively incorporate time-varying treatment effect assessments and restrict efficacy claims to molecularly defined HRR-deficient populations unless biomarker-unselected benefit is robustly demonstrated.