Study of Durvalumab and Tremelimumab After Radiation for Microsatellite Stable Metastatic Colorectal Cancer Progressing on Chemotherapy

The FC-9 study is designed as a phase II, open label, single arm study of the dual immune checkpoint blockade with the combination of durvalumab and tremelimumab following hypofractionated palliative radiation in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC) who have progressed on chemotherapy. The primary aim is to determine the anti-tumor efficacy of the dual immune checkpoint blockade with durvalumab plus tremelimumab. The secondary aims are to determine the clinical benefit rate, duration of response, tolerability and correlates of response. Tumor response at unirradiated target lesions will be measured at baseline and every 2 cycles using RECIST 1.1. Following three doses of hypofractionated palliative radiation (Days -2, -1, and Day 0 prior to Cycle 1), patients will receive the combination of tremelimumab (75 mg IV infusion) and durvalumab (1500 mg IV infusion) on Day 1 for 4 cycles. Beginning with Cycle 5 through Cycle 24, patients will receive durvalumab alone (1500 mg/IV infusion) on Day 1 of each 28 day cycle. The sample size will be between 12 and 21 evaluable patients. Twelve evaluable patients will be treated in the first stage of the study. If there are no responses among the 12 evaluable patients, the study will be terminated. If the study goes on to the second stage, a total of 21 evaluable patients will be studied. Submission of tumor tissue and blood samples for FC-9 correlative science studies will be a study requirement for all patients. Requirements will include archived tumor samples from the diagnostic biopsy; additional biopsies of fresh tissue from an accessible lesion prior to radiation therapy and after 2 cycles of study therapy; and blood sample collections.