PD1/PD-L1 targeting in advanced soft-tissue sarcomas: a pooled analysis of phase II trials

Immune checkpoint inhibitors, especially the programmed cell death receptor-1/ligand 1 (PD-1/L1) inhibitors, displayed promising efficacy in several solid tumor types and hematological malignancies. Data related to their activity in soft-tissue sarcomas (STS) are scarce. We performed a pooled analysis of clinical trials investigating a PD1 or PD-L1 antagonist in patients with advanced STS. Three hundred eighty-four patients were included in the pooled analysis; of those, 153 (39.8%) received a PD1/PD-L1 antagonist as a single agent. In patients treated with anti-PD1/PDL1 as a single agent, the overall response rate (ORR) and non-progression rate (NPR) were 15.1% and 58.5% respectively. In patients treated with a combination regimen, the ORR and NPR were 13.4% and 55.8% respectively. Analysis by histological subtype revealed that patients with alveolar soft part sarcoma and undifferentiated pleomorphic sarcoma exhibited the highest response rates and leiomyosarcoma the lowest. PD-L1 expression rate was low and inconsistently associated with objective response. PD-1/PD-L1 antagonists have limited activity in unselected STS. Future studies should implement histology and immune-based stratification of STS in their design as well as sequential blood and tissue sampling to better understand the mechanisms of resistance and response given sarcomas inherent heterogeneity.