Real-world experience with pembrolizumab in patients with advanced soft tissue sarcoma

BACKGROUND: The goal of this study was to retrospectively analyze the efficacy and safety of pembrolizumab in the real-world treatment of soft tissue sarcoma (STS). METHODS: We analyzed 38 patients who suffered from STS and received pembrolizumab treatment from July 2017 to December 2018 in our hospital. We investigated the influence of clinical characteristics, treatment timing, and treatment protocol on objective response rate (ORR). We also investigated the factors affecting overall survival (OS) and progression-free survival (PFS), as well as the occurrence of severe adverse events (SAEs). RESULTS: The overall ORR was 19.4% (7/36). The ORRs of patients who received pembrolizumab treatment as first-line, second-line, and third-line therapy were 42.9% (3/7), 25.0% (4/16), and 0% (0/13), respectively, which showed marginal significance (P=0.052). Four patients (11.1%) maintained a complete response (CR) or partial response (PR) for at least 6 months with pembrolizumab monotherapy, or after withdrawal of chemotherapy or targeted therapy regimens. The median PFS was 2.9 months [95% confidence interval (CI): 2.4–3.4 months] and the median OS was 12.0 months (95% CI: 10.2–13.8 months). Cox regression analysis showed that treatment time was an independent factor affecting PFS (P=0.041), while Eastern Cooperative Oncology Group (ECOG) performance status (PS) score was the only independent factor affecting OS (P=0.028). CONCLUSIONS: In the real world, the effectiveness of pembrolizumab in the treatment of STS was low. Some subtypes showed a limited response to pembrolizumab, including alveolar soft part sarcoma (ASPS), undifferentiated pleomorphic sarcoma (UPS), exoskeletal chondrosarcoma (ESCS), and angiosarcoma (AS), while the response in leiomyosarcoma (LMS) was low. Combination therapy may increase the risk of SAEs, especially when combined with pazopanib.