Impact of treatment intensification with abiraterone on fracture-related hospitalisation in newly diagnosed prostate cancer: a secondary analysis of two randomised phase 3 Trials within the STAMPEDE trial platform.

Background

Prostate cancer (PCa) patients are at increased fracture risk due to the need for androgen deprivation therapy (ADT) and progressive bone metastases. Previous meta-analyses of randomised controlled trials suggest that androgen receptor pathway inhibitors (ARPIs) increase fracture risk.

Objective

We assessed the impact of abiraterone-based treatment intensification on fracture-related hospitalisation (FRH) within the STAMPEDE trial platform. Design, setting and participants We performed a secondary analysis of two STAMPEDE trials in patients with high-risk non-metastatic (M0) or metastatic (M1) disease.

Interventions

Patients were allocated to either standard of care (SOC) or SOC plus abiraterone with prednisolone (AAP) or, in a later comparison, SOC+AAP with enzalutamide (Enza).

Outcome measurements and statistical analysis

A prespecified coding framework within Hospital Episode Statistics (HES) identified FRHs. Flexible parametric competing-risk models estimated 5-year cumulative incidence of FRH and sub-distribution hazard ratios (SDHR), with death as a competing risk.

Outcome measurements and statistical analysis

Between Nov 2011 and Mar 2016, 3893 patients were randomised to the STAMPEDE AAP±Enza trials. Linked HES data were available for 3102 patients in England. In M1 disease, 5-year FRH incidence was significantly lower with SOC + AAP than SOC alone (22% vs 30%; SDHR 0.77, 95%CI 0.59-0.99; p = 0.04) and with SOC + AAP + Enza than SOC alone (28% vs 38%; SDHR 0.69, 95%CI 0.54-0.88; p = 0.002). No significant difference was observed in M0 patients. Limitations include potential under-estimation of total fracture burden by exclusion of non-hospitalised fractures, lack of baseline assessment of fracture risk including bone mineral density, and longitudinal use of bone-protective therapy.

Conclusions

Abiraterone-based treatment intensification did not increase FRH compared to SOC alone. In M1 disease, abiraterone reduced rather than augmented fracture risk, most plausibly reflecting improved metastatic bone disease control.