A Randomized Trial of Pembrolizumab & Radiotherapy Versus Radiotherapy in High-Risk Soft Tissue Sarcoma of the Extremity

This is a multicenter, randomized phase II trial with an initial safety run-in to test the safety and efficacy of neoadjuvant pembrolizumab with image-guided radiotherapy and adjuvant pembrolizumab compared to radiation therapy alone in patients with clinically localized extremity soft tissue sarcoma at high risk for developing metastatic disease (tumor size \> 5 cm, intermediate- to high-grade; approximately 50% risk for distant disease at 2 years). Histologies will be limited to undifferentiated pleomorphic sarcoma and dedifferentiated/pleomorphic liposarcoma based on preliminary data from SARC028. Other terms for undifferentiated pleomorphic sarcoma may include, but are not limited to. pleomorphic undifferentiated sarcoma, unclassified spindle cell sarcoma, spindle cell sarcoma not otherwise specified, pleomorphic spindle cell sarcoma, pleomorphic fibroblastic sarcoma, undifferentiated high-grade pleomorphic sarcoma, pleomorphicsarcoma with prominent inflammation, pleomorphic sarcoma with giant cells, malignant fibrous histiocytoma (including storiform-pleomorphic and inflammatory subtypes), fibrosarcoma, and myxofibrosarcoma (located deep to the fascia in muscle). Radiation therapy with three cycles of pembrolizumab will be administered as neoadjuvant therapy for patients randomized to the experimental arm. These patients will also receive up to fourteen cycles of adjuvant pembrolizumab after surgical resection. Patients in the standard of care arm will receive neoadjuvant radiotherapy (50 Gy in 25 fractions) followed by surgical resection as in RTOG 0630.