Effects of liver metastases on efficacy of immune checkpoint blockade in treatment refractory, metastatic colorectal cancer (CRC): CCTG CO.26

3600 Background: Immune checkpoint blockade has limited activity in microsatellite-stable (MSS) or mis-match repair proficient (pMMR) CRC. Recent findings suggest that immunotherapy efficacy may be modulated by the presence of liver metastases. We conducted a retrospective analysis of the Canadian Cancer Trials Group (CCTG) CO.26 study to investigate the relationship between the presence of liver metastases and activity of immune checkpoint blockade. Methods: The CCTG CO.26 study was a randomized phase II study (NCT02870920). Pts with treatment refractory CRC were randomized to durvalumab, tremelimumab and best supportive care (BSC) or BSC alone in a 2:1 fashion. Treatment consisted of durvalumab (1500 mg) q 28 days and tremelimumab (75 mg) q 28 days for the first 4 cycles. The primary endpoint was overall survival (OS) and a two-sided p-value