Phase 2 study of pembrolizumab in combination with azacitidine in subjects with metastatic colorectal cancer

3054 Background: Microsatellite stable (MSS) metastatic colorectal cancer (mCRC) has relatively poor tumoral infiltration of CD8+ T cells and is resistant to pembrolizumab (Pembro) when compared to MSI-H mCRC. DNA hypomethylating agent induces epigenetic expression of multiple genes including cancer-testis antigens in CRC, which are recognized by cytotoxic CD8+ T cells in vitro and in vivo. This trial tested whether concurrent treatment with azacitidine (Aza) could enhance the anti-tumor activity of Pembro. Methods: This is a phase 2 trial to evaluate anti-tumor activity and safety of Pembro plus Aza in patients (pts) with previously treated mCRC without any further standard chemotherapy option. Pts received Pembro 200 mg IV on day 1 of each cycle Q3W and Aza 100 mg daily SQ injection on days 1-5 of each cycle Q3W. Primary endpoint was response rate (ORR) using RECIST v1.1. Secondary endpoints included progression-free survival (PFS) and overall survival (OS). Tumor tissues were collected for correlative studies. Results: Thirty-one pts were enrolled [median age, 61 years (range, 30-79); 17 M/14 F; ECOG PS 0/1 (58%/42%); 30 pts with MSS mCRC]. Pts received at least 2 lines of prior systemic chemotherapy for mCRC (median, 3; range, 1-5). Thirty pts received at least one dose of study therapy (median, 3 cycles; range, 1-8). Ten pts could not complete the first 3 cycles due to rapid symptomatic tumor progression. One pt with MSS mCRC achieved PR and 3 pts had SD as best response. The ORR was 3% (1/30; 95% CI, 0.1-17%). Seven pts with PD at the end of cycle 3 continued on study therapy, and 2 pts had stabilization of tumor progression. Median PFS was 2.1 months (95% CI, 1.8-2.8), and median OS was 6.2 months (95% CI, 3.5-8.7). While treatment-related adverse events (TRAEs) were reported in 63% of pts, most of the TRAEs were Gr 1/2 (96%). Frequent TRAEs possibly related to Aza were anemia (n = 5), constipation (n = 5), and leukopenia (n = 4); and possibly related to both Aza and Pembro were nausea (n = 5) and fatigue (n = 5). Gr 3 TRAEs included anemia (n = 1), ALT elevation (n = 1), and alkaline phosphatase elevation (n = 1). Conclusions: Pembro plus Aza is feasible with a tolerable safety profile but appears to have minimal anti-tumor effect for MSS mCRC. Clinical trial information: NCT02260440.