Randomised phase II study of second-line olaratumab with mitoxantrone/prednisone versus mitoxantrone/prednisone alone in metastatic castration-resistant prostate cancer
Abstract
Introduction: Platelet-derived growth factor receptor-alpha (PDGFR alpha) is expressed in primary prostate adenocarcinoma and in associated skeletal metastases. Olaratumab is a fully human monoclonal antibody that binds PDGFR alpha and blocks downstream signalling.
This phase II study assessed the efficacy and safety of olaratumab in combination with mitoxantrone and prednisone (M/P) versus M/P alone in patients with metastatic castration-resistant prostate cancer (mCRPC) who progressed after docetaxel. Methods: Patients were randomised to receive 21-d cycles of olaratumab (15 mg/kg, Days 1 and 8) plus mitoxantrone (12 mg/m(2), Day 1) and prednisone (5 mg, twice daily) or M/P alone.
Progression-free survival (PFS) was the primary end-point. Secondary end-points included overall survival (OS), safety, and circulating tumour cell (CTC) counts.
Results: A total of 123 patients were randomised, 63 to olaratumab + M/P and 60 to M/P. Median PFS was 2.3 months for olaratumab + M/P and 2.4 months for M/P (hazard ratio [HR] = 1.29; 95% confidence interval [CI] = 0.87-1.90).
Median OS was 14.2 months for olaratumab + M/P and 12.8 months for M/P (HR = 1.08; 95% CI = 0.72-1.61). Both treatment arms had similar toxicity profiles; neutropenia (24% versus 15%), anaemia (13% versus 14%) and fatigue (11% versus 9%) (olaratumab + M/P versus M/P, respectively) were the most common grade >= 3 events.
High CTC count was associated with poorer OS in both arms. Patients with very high cell counts (>37 cells/7.5 ml) exhibited improved OS with olaratumab + M/P (interaction P = 0.043).
Conclusions: Olaratumab + M/P had an acceptable safety profile but did not improve the efficacy of M/P chemotherapy. Further study with selected patient populations and earlier in the disease course might be considered.