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.

Olaratumab for advanced soft tissue sarcoma

INTRODUCTION

Olaratumab is a humanized IgG1 monoclonal antibody that blocks the platelet-derived growth factor receptor alpha (PDGFRα). Its antagonistic behavior inhibits the receptor's tyrosine kinase activity, thereby, turning off the downstream signaling cascades responsible for soft tissue sarcoma tumorigenesis. In October 2016, olaratumab received Food and Drug Administration (FDA) approval for its use in combination with doxorubicin for treatment of advanced soft tissue sarcoma. Areas covered: This drug profile takes a comprehensive look at the clinical studies leading to FDA approval of olaratumab as well as its safety and efficacy as a front-line treatment option for sarcoma patients. The literature search was primarily conducted using PubMed. Expert commentary: The combination of olaratumab plus doxorubicin has provided a new front-line therapeutic option for soft tissue sarcoma patients. An open-label phase Ib and randomized phase II trial in patients with advanced soft tissue sarcoma demonstrated that the addition of olaratumab to doxorubicin prolonged progression-free survival by 2.5 months and overall survival by 11.8 months when compared to doxorubicin alone. Of importance, this clinically meaningful increase in overall survival did not come at the expense of a significantly greater number of toxicities. A phase III confirmatory trial (ClinicalTrials.gov Identifier NCT02451943) will be completed in 2020.