ENCORE 601: A phase II study of entinostat (ENT) in combination with pembrolizumab (PEMBRO) in patients with melanoma.

9529Background: Entinostat is an oral, class I selective histone deacetylase inhibitor shown preclinically to enhance immune checkpoint inhibitor activity by regulation of immune suppressor cells in the tumor microenvironment. ENCORE 601 is designed to evaluate safety and efficacy of ENT in combination with PEMBRO. Phase 1b identified ENT 5 mg PO weekly and PEMBRO 200 mg IV every 3 weeks as the recommended Phase 2 dose for further investigation. Methods: Phase 2 of ENCORE 601 employs a Simon 2-stage design to assess activity across 3 cohorts: 1) NSCLC not previously treated with a PD-1/L1 blocking antibody, 2&3) NSCLC & melanoma previously progressing on or after a PD-1/L1 blocking antibody. Patients were enrolled irrespective of PD-L1 expression levels. The primary endpoint is ORR as assessed by irRECIST. Results of the first stage of Cohort 3 are reported. Criteria for advancing to Stage 2 are ≥2 responses out of 13 evaluable patients. Results: Stage 1 enrollment has been completed (n = 13). All patient...