Phase II trial of pazopanib in patients with metastatic or unresectable chemoresistant sarcomas: A Japanese Musculoskeletal Oncology Group study

Alveolar soft part sarcoma (ASPS), epithelioid sarcoma (ES), and clear cell sarcoma (CCS) are known to be chemoresistant tumors. The aim of this study was to investigate the effect of pazopanib on these chemoresistant tumors. This study is designed as a single‐arm, multicenter, investigator‐initiated phase II trial. Patient enrollment was undertaken between July 2016 and August 2018 at 10 hospitals participating in the Japanese Musculoskeletal Oncology Group. The primary end‐point is the CBR (CBR, including complete or partial response and stable disease) at 12 weeks after treatment with pazopanib according to RECIST. Eight patients were enrolled within the period. The histological subtypes were 5 ASPS, 2 ES, and 1 CCS. The median follow‐up period was 22.2 (range, 4.9‐24.9) months. All patients initially received pazopanib 800 mg once daily. The CBRs were 87.5% (7 of 8) and 75.0% (6 of 8) according to RECIST and Choi criteria at 12 weeks after pazopanib treatment, respectively. The CBRs at 12 weeks according to RECIST were 80.0%, 100.0%, and 100.0% in ASPS, ES, and CCS, respectively. Partial response was observed in 1 ASPS according to RECIST and 3 ASPS and 1 ES according to Choi criteria at 12 weeks after pazopanib treatment. This study documented antitumor activity of pazopanib, especially in ASPS. These results support the frontline use of pazopanib for ASPS. Prospective data collection is desired using both RECIST and Choi criteria for these rare chemoresistant tumors.