Treatment for poor prognosis metastatic castration-resistant prostate cancer (mCRPC) includes taxane chemotherapy and androgen receptor pathway inhibitors (ARPI). We sought to determine optimal treatment in this setting.
Patients and Methods
This multicentre, randomised, open-label, phase 2 trial recruited patients with ARPI-naïve mCRPC and poor prognosis features (presence of liver metastases, progression to mCRPC after <12 months of androgen deprivation therapy, or ≥4 of 6 clinical criteria). Patients were randomly assigned 1:1 to receive cabazitaxel plus prednisone (Group A) or physician’s choice of enzalutamide or abiraterone plus prednisone (Group B) at standard doses. Patients could cross-over at progression. The primary endpoint was clinical benefit rate for first-line treatment (defined as PSA response ≥50%, radiographic response, or stable disease ≥12 weeks).
95 patients were accrued (median follow-up 21.9 months). First-line clinical benefit rate was greater in Group A versus B (80% vs 62%, p=0.039). Overall survival was not different between Group A and B (median 37.0 vs 15.5 months, HR=0.58, p=0.073) nor was time to progression (median 5.3 vs 2.8 months, HR=0.87, p=0.52). The most common first-line treatment-related grade ≥3 adverse events were neutropenia (cabazitaxel 32% vs ARPI 0%), diarrhea (9% vs 0%), infection (9% vs 0%) and fatigue (7% vs 5%). Baseline circulating tumour DNA (ctDNA) fraction above the cohort median and on-treatment ctDNA increase were associated with shorter time to progression (HR = 2.38, p < 0.001; HR = 4.03, p < 0.001). Patients with >30% ctDNA fraction at baseline had markedly shorter overall survival than those with undetectable ctDNA (HR = 38.22, p < 0.001).
Cabazitaxel was associated with a higher clinical benefit rate in patients with ARPI-naïve poor prognosis mCRPC. CtDNA abundance was prognostic independent of clinical features, and holds promise as a stratification biomarker.