Defining more precisely the effects of docetaxel plus ADT for men with mHSPC: Meta-analysis of individual participant data from randomized trials.

5070 Background: Adding docetaxel to androgen deprivation therapy(ADT) improves survival in metastatic, hormone-sensitive prostate cancer (mHSPC), but uncertainty remains about who benefits most. To investigate this thoroughly and reliably, the STOPCAP M1 collaborationconducted a meta-analysis of individual participant data (IPD) from relevant trials. Methods: Methods were included in a registered protocol ( CRD42019140591 ). Updated IPD from the GETUG-15, CHAARTED and STAMPEDE trials were harmonised and checked. The main outcomes were overall survival (OS), progression-free survival (PFS) and failure-free survival (FFS). Overall pooled effects were estimated using intention-to-treat, 2-stage, fixed-effect meta-analysis, adjusted for age, PSA, Gleason sum score, performance status, and timing of metastatic disease (missing covariate values imputed), with 1-stage and random-effects sensitivity analyses. We assessed subgroup effects using 2-stage, fixed-effect meta-analysis of within-trial interactions, adjusted for the same covariates. We based these on PFS to maximise power, and OS whenever interactions were found. To explore multiple subgroup interactions, and to derive subgroup-specific absolute treatment effects, we used 1-stage, flexible parametric modelling and standardisation. Results: We obtained IPD for all 2261 men randomised, with median FU of 6 years (all patients). There were clear relative benefits of docetaxel on OS (HR = 0.79, 95% CI 0.70 to 0.88, p<0.0001), PFS (HR = 0.70, 95% CI 0.63 to 0.77, p<0.0001) and FFS (HR = 0.64, 95% CI 0.58 to 0.71, p<0.0001). With evidence of non-proportional hazards, we also estimated 5-year absolute differences: OS 10% (95% CI 6 to 15%), PFS 9% (95% CI 5 to 13%) and FFS 9% (95% CI 6 to 12%). The relative effect of docetaxel on PFS differed by volume of metastases (interaction p=0.027; high volume HR = 0.60, 95% CI 0.52 to 0.68; low volume HR = 0.78, 95% CI 0.64 to 0.94), and timing of metastatic disease (interaction p=0.077; synchronous HR = 0.67, 95% CI 0.60 to 0.75; metachronous HR = 0.89, 95% CI 0.67 to 1.18). OS results were similar. When metastatic disease volume and timing were combined, docetaxel appeared to improve PFS and OS for all men, except those with low volume, metachronous disease (Table). Conclusions: This IPD meta-analysis provides the most detailed assessment of the effects of docetaxel for mHSPC, and suggests that men with low volume, metachronous disease should be managed differently to those with other types of metastatic disease. [Table: see text]