BACKGROUND: Investigation remains incomplete regarding potential variations in the effect of androgen receptor pathway inhibitors, including apalutamide, based on baseline tumor burden in patients with metastatic castration-sensitive prostate cancer (mCSPC). METHODS: The authors analyzed individual participant-level data from 1052 patients with mCSPC who were randomized in the TITAN trial (apalutamide vs. placebo, both with androgen-deprivation therapy). Outcomes included radiographic progression-free survival (PFS), second PFS (PFS2), and overall survival (OS). Multivariable Cox proportional hazards regression models, with and without restricted cubic splines, were used to determine the association between apalutamide benefit and bone metastasis count or visceral metastasis. Subgroup treatment effects were quantified based on inverse probability of treatment weighting-adjusted hazard ratios (HRs). RESULTS: Analysis using restricted cubic splines indicated that apalutamide provided less benefit for PFS2 and OS in patients with fewer bone metastases. The authors also found evidence of a heterogeneous effect of apalutamide on PFS2 and OS between patients with two or less bone metastases and those with three or more bone metastases. In patients who had two or less bone metastases, there was no evidence of a benefit from apalutamide for radiographic PFS (HR, 0.65; 95% confidence interval [CI], 0.35-1.22), PFS2 (HR, 1.18; 95% CI, 0.66-2.12), or OS (HR, 1.05; 95% CI, 0.60-1.83). No evidence of an association was noted between visceral metastasis and apalutamide benefit. CONCLUSIONS: The addition of apalutamide to androgen-deprivation therapy may provide less benefit in patients with mCSPC who have fewer bone metastases. Counting baseline bone metastases may help identify optimal candidates for apalutamide treatment of mCSPC. CLINICAL TRIALS REGISTRATION: NCT02489318 PLAIN LANGUAGE SUMMARY: In an analysis of individual participant data from a trial (the TITAN trial) in patients with metastatic (spreading) castration-sensitive prostate cancer, treatment intensification based on the addition new drugs to standard androgen-deprivation therapy (ADT) was analyzed and compared with the effects in patients who received only standard ADT. Compared with ADT alone, the survival benefit of adding the new drug apalutamide to standard ADT varied according to the number of bone metastases, but no association was observed between the spread of cancer to soft tissues and organs and a survival benefit from adding apalutamide. The results indicate that counting the number of bone metastases may help identify which patients with metastatic castration-sensitive prostate cancer are optimal candidates for treatment intensification with the addition of apalutamide to standard ADT.

2nd Department of Urology Center of Postgraduate Medical Education Warsaw Poland

Department of Clinical Biostatistics Institute of Science Tokyo Tokyo Japan

Department of Medical Oncology National Cancer Center Hospital East Chiba Japan

Department of Urology 2nd Faculty of Medicine Charles University Prague Czech Republic

Department of Urology Comprehensive Cancer Center Medical University of Vienna Vienna Austria

Department of Urology The Jikei University School of Medicine Tokyo Japan

Department of Urology University of Texas Southwestern Dallas Texas USA

Department of Urology Vita Salute San Raffaele University Milan Italy

Department of Urology Weill Cornell Medical College New York New York USA

Division of Surgery and Interventional Science University College London London UK

Karl Landsteiner Institute of Urology and Andrology Vienna Austria

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