Toulmonde M, et al. - The efficacy and safety of programmed cell death protein 1 (PD-1) targeting in combination with metronomic chemotherapy in sarcomas were determined. In selected soft-tissue sarcoma and gastrointestinal stromal tumor, findings revealed a limited activity of PD-1 inhibition. This could be due to an immunosuppressive tumor microenvironment resulting from macrophage infiltration and indoleamine 2,3-dioxygenase 1 pathway activation.