Background: The optimal treatment for patients with advanced dedifferentiated (DD) liposarcoma (LPS) remains uncertain. Single agents which are most effective include doxorubicin and ifosfamide but, as with soft tissue sarcomas (STS) in general, objective response rates (ORR) and progression free survival (PFS) are very modest. Cabazitaxel exerts its effect through inhibition of microtubular disassembly and has been shown to be relatively safe, effective and well-tolerated. EORTC 1202 assessed whether cabazitaxel demonstrated sufficient antitumor activity in patients with metastatic or inoperable locally advanced DD LPS to justify further investigation in a phase III setting. Methods: This was an international multi-center, open label single arm phase II trial. Eligible patients with metastatic or inoperable locally advanced DD LPS were treated with cabazitaxel 25mg/m² IV infusion over 1 hour every 21 days. Primary endpoint was PFS rate at 12 weeks assessed by local investigator per RECIST 1.1. Based on a Simon two-stage design, at least 4 out of 17 (Stage 1) and 11 out of 37 (Stage 2) eligible and evaluable patients who are progression-free at 12 weeks were needed. Results: Forty patients were registered by 10 institutions in 4 countries between March 2015 and March 2019, with 2 patients being ineligible. Among the 38 eligible patients who started treatment, 3 (7.5 %) were still on treatment at the time of analysis. The number of cycles ranged from 1 to 30, with a median of 5; 26 patients (65%) received at least 4 cycles of cabazitaxel. Among the first 17 (Stage 1) and 37 (Stage 2), 11 and 20 patients were progression-free at 12 weeks respectively, satisfying the study decision rules. The PFS rate at 12 weeks for all 38 eligible patients was 52.6% (conditional 1-sided 95 % CI 38.3 – 100). Two patients (5.3%) achieved a confirmed partial response (PR) and 23 stable disease (SD) (60.5%). Disease control (PR+SD) was achieved in 25 patients (65.8%). Median PFS was 7.4 months (95%CI 2.8-10.3). The most common cabazitaxel -related grade >3 adverse events in all 40 registered patients were neutropenia (60%), febrile neutropenia (25%), fatigue (12.5%), and anemia (10%). There were no cabazitaxel-related deaths. Conclusions: EORTC 1202 met its primary endpoint, with 20/37 pts (54%) being progression-free at 12 weeks. Results of this trial confirm activity of cabazitaxel in patients with metastatic or inoperable locally advanced DD LPS and warrant further exploration of the drug. Clinical trial information: NCT01913652.