Data from the Alliance A091401 study of nivolumab and ipilimumab suggests this may also be true for sarcoma.8 In a primary versus transplant preclinical mouse model of UPS, primary tumors were resistant to radiotherapy and dual-checkpoint blockade with PD-1 and CTLA-4.28 In that study, single-cell sequencing indicated low numbers of activated T cells in primary tumors. Here, CTLA4 is linked to undifferentiated pleomorphic sarcoma.