Background: Soft tissue sarcomas (STS) are a rare type of malignancy, which comprises of a variety of histologies. Chemotherapy is the standard treatment for patients with advanced STS. Doxorubicin alone or in combination with ifosfamide is widely accepted as the first-line chemotherapy for advanced STS. While a combination with gemcitabine and docetaxel is regarded as a standard regimen of the second-line chemotherapy after failure of doxorubicin-based first-line regimen, the efficacy is not sufficient. Trabectedin, eribulin, and pazopanib are the candidates of the second-line chemotherapy for advanced STS, although there is no clear evidence showing which is better among those agents. The purpose of this clinical trial conducted by Bone and Soft Tissue Tumor Study Group of Japan Clinical Oncology Group (JCOG) is to determine the most promising regimen among trabectedin, eribulin and pazopanib as the test arm regimen in the future phase III trial of the second-line treatment for patients with advanced STS. Methods: The study, JCOG1802, is a multicenter, selection design, randomized phase II trial comparing trabectedin (1.2 mg/m² IV, every 3 weeks), eribulin (1.4 mg/m² IV, days 1 and 8, every 3 weeks) and pazopanib (800 mg PO, everyday) for patients with unresectable or metastatic STS refractory to doxorubicin-based first-line chemotherapy. Eligibility criteria include 16 year-old or older, unresectable and/or metastatic STS, an exacerbation within 6 months prior to registration, histological diagnosis of STS other than Ewing sarcoma, well-differentiated liposarcoma and myxoid liposarcoma, a history of chemotherapy for STS other than doxorubicin-based regimen, ECOG (Eastern Cooperative Oncology Group) performance status 0 to 2, and sufficient organ function. Primary endpoint is progression-free survival (PFS), and secondary endpoints include overall survival, disease-control rate, response rate, and adverse events. To select the most promising regimen in median PFS (3 months in the worst regimen and 4 months in the best regimen) with a probability of at least 80%, a total of 120 patients will be enrolled from 37 institutions in Japan. After JCOG1802, a subsequent phase III trial comparing the winner of this study and a combination of gemcitabine and docetaxel will be planned. The study was activated at December 5, 2019 and 22 of planned 120 patients have been enrolled as of February 15, 2021. Clinical trial information: jRCTs031190152.