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Safety and clinical activity of durvalumab monotherapy in patients with microsatellite instability–high (MSI-H) tumors.

670 Background: MSI-H tumors have shown to be responsive to PD-1 inhibitor therapy. We evaluated the anti-PD-L1 mAb durvalumab in patients with MSI-H tumors, in two ongoing studies: a phase 1/2, multicenter, open-label study in patients with advanced solid tumors, and a phase 2 single-center study in patients with advanced colorectal cancer (CRC). Methods: Patients with MSI-H tumors (determined locally by immunohistochemistry or sequencing) received durvalumab 10 mg/kg IV every 2 weeks for 12 months or until confirmed progressive disease, whichever was first. Objectives were to evaluate safety and antitumor activity (per investigator-assessed RECIST v1.1). Results: As of Oct 16, 2017, 62 MSI-H patients (97% with prior anti-cancer therapy) received treatment in the multicenter study; median duration of follow-up was 29 months. Treatment-related adverse events (TRAEs) occurred in 37 patients (60%), most commonly diarrhea (15%), asthenia (11%), fatigue (11%), nausea (10%), and hypothyroidism (10%). Grade 3/4 TRAEs occurred in 2 patients (3%). There were no deaths or treatment discontinuations due to TRAEs. Objective response rates (ORR) were 23% for the total population and 22% for patients with CRC; 9 of 14 responders were ongoing at data cutoff. As of Sep 13, 2018, 11 patients with MSI-H CRC were treated in the single-center study; median duration of follow-up was 30 months. One patient discontinued treatment due to treatment-related aseptic meningitis (resolved with steroids); response rate and survival were similar to the multicenter study (Table). Conclusions: Durvalumab had a tolerable safety profile, and showed promising antitumor activity and overall survival in patients with MSI-H tumors. Clinical trial information: NCT01693562 and NCT02227667. [Table: see text]