Pazopanib in the advanced and rare subtypes of soft tissue sarcoma: Russian Sarcoma Group study.

e23528 Background: Sarcoma is a heterogeneous group of tumors that arise from connective tissue. The most frequent localizations of primary tumors are soft tissues and bones of the extremities, and the lungs is the most common localization of metastases. Pazopanib is an antineoplastic agent, multi-kinase inhibitor that retards angiogenesis in tumor tissues and has been shown to be effective in the treatment of patients with advanced sarcoma. Median progression-free survival was 4,6 months (95% CI 3,7–4,8) for pazopanib compared with 1,6 months (0,9–1,8) for placebo in the PALETTE clinical trial. This study designed to detect epidemiology data as well as the pazopanib efficiency for rare sarcoma subtypes. Methods: We collected data from 109 cases with 20 different sarcoma histotypes and 15 localizations, at N.N. Blokhin National Medical Research Center of Oncology from 2018 till 2020. Disease was histologically confirmed by a sarcoma pathologist. The average age of patients was 47.8 years and the women and men ratio was about 2:1. Patients received pazopanib 800 mg once daily and passed control examinations every 2 or 3 months (CT/MRI). Treatment response was assessed by RECIST criteria. Results: The most frequent localizations of primary tumors were the soft tissues of the extremities (39.6%), the uterus (16.9%) and the retroperitoneum (13.2%). The main histological subtypes were leiomyosarcoma (33.6%) and synovial sarcoma (14.9%). There were also included such types like a embryonal rhabdomyosarcoma, chondrosarcoma, Ewing tumors, EHE, alveolar soft part sarcoma, PEComa, clear cell sarcoma, adamantinoma, solitary fibrous tumor, epithelioid sarcoma and myxoid liposarcoma. The majority of patients (61%) received more than 2 of therapy. The average duration of therapy was 7.5 months. Best tumor response by RECIST was as follows: complete response 0 (0%), partial response 2 (2%), stable disease 81 (88,3%), progression disease 25 (27,3%) cases. Median progression-free survival was 8 months (95% CI 6,7-9,2) for pazopanib. Median overall survival was not reached. Overall pazopanib was well tolerated, except one case with SAE. Conclusions: In this study we observed pazopanib efficiency in a rare for pazopanib sarcoma subtypes such as myxoid liposarcoma (1 PR), PEComa, adamantinoma, embryonal rhabdomyosarcoma, malignant peripheral nerve sheath tumor and Ewing tumors. Also our study confirms pazopanib long-term disease control in alveolar soft part sarcoma, clear cell sarcoma, leiomyosarcoma, synovial sarcoma and undifferentiated pleomorphic sarcoma which explains median PFS 8 months.