Phase 1 study of olaratumab plus doxorubicin in Japanese patients with advanced soft-tissue sarcoma

Olaratumab, a monoclonal antibody targeting human platelet-derived growth factor receptor α, plus doxorubicin significantly improved overall survival in patients with advanced soft-tissue sarcoma (STS) in a prior phase 1b/2 randomized trial. Subsequent exposure-response analysis suggested that higher olaratumab exposures earlier might improve outcomes in patients at risk of early disease progression. This phase 1 study (3 treatment cohorts; minimum 6 patients each) investigated the safety, pharmacokinetics and antitumor activity of olaratumab plus doxorubicin in Japanese patients with STS. Patients received olaratumab 15 mg/kg on Days 1 and 8 during each 21-day cycle until disease progression. Patients in Cohort 3 received a 20 mg/kg loading dose of olaratumab in Cycle 1. Doxorubicin was administered for up to 6 cycles. Patients in Cohort 1 received doxorubicin 25 mg/m² on Days 1, 2 and 3. Patients in Cohorts 2 and 3 received doxorubicin 75 mg/m² on Day 1. One patient in Cohort 2 experienced a dose-limiting toxicity of Grade 3 febrile neutropenia. Most treatment-emergent adverse events were of mild and moderate severity, and were known doxorubicin toxicities. Olaratumab serum concentrations in Cohort 3 reached a steady-state exceeding the target level in Cycle 1. Partial response was confirmed in 4 patients (2 each in Cohorts 2 and 3). Olaratumab plus doxorubicin had an acceptable safety profile in patients with STS. A loading dose of olaratumab 20 mg/kg was effective for achieving minimum serum concentrations above the target trough level in Cycle 1.