Data from the SARC028 trial have shown the encouraging activity of pembrolizumab in patients with UPS and DDLS, but poor response rates in synovial sarcoma, leiomyosarcoma, and osteosarcoma.7,11,14 The use of immunotherapy in sarcoma patients is beset with the same issues that arise with other tumor types, namely an absence of useful predictive markers for patient stratification and lack of clarity on which alternative options to use in those refractory to anti-PD-1- and/or anti-CTLA-4-based regimens. The gene discussed is CTLA4; the disease is osteosarcoma.