Background: Immune-suppressing molecules can be exploited by tumor cells to suppress immune responses to cancer. Programmed cell death-1 (PD-1) is an inhibitory regulator of T-cell activation. The ligand to PD-1, PD-L1, is upregulated in several tumor types. MEDI4736 is a human IgG1 mAb that blocks PD-L1 binding to PD-1 and CD80 with high affinity and selectivity. Methods: This Phase 1, multicenter, open-label study (NCT01938612) is evaluating the safety, PK, and clinical activity of MEDI4736 in Japanese patients (pts) with advanced solid tumors. Pts ( ≥ 20 years) with ECOG performance status 0–1 who are refractory or intolerant to standard treatment or for whom no standard treatment exists are eligible. MEDI4736 was given IV every 2, 3, or 4 wks (q2/3/4w) using a 3+3 dose escalation, followed by a dose-expansion phase that includes further pts at or below the maximum tolerated dose. Treatment continues for up to 12 months; retreatment is possible upon progression after 12 months. Disease response was assessed by RECIST v1.1. Results: As of 27 November 2014, 22 pts were enrolled across 5 dose levels. Drug-related adverse events (AEs) ≥ Grade (G) 2 were pneumonitis (G2; 3 mg/kg q2w), oral stomatitis (G2; 3 mg/kg q2w), constipation (G2; 3 mg/kg q2w), hypothyroidism (G2; 15 mg/kg q3w), eruption (G2, 20 mg/kg q4w), skin atheroma (G2, 1 mg/kg q2w), mucositis (G2; 3 mg/kg q2w), and serum-free triiodothyronine decreased (FT3; G3; 10 mg/kg q2w); all n = 1. There were no G4 drug-related AEs. G2 pneumonitis and G3 low serum FT3 were considered serious drug-related AEs. 1 pt discontinued due to an AE; G1 pneumonitis. No drug-related deaths or dose-limiting toxicities (DLTs) were reported. Of 19 evaluable pts with ≥ 1 post-baseline CT assessment, 1 pt (10 mg/kg q2w) had a partial response, and 6 pts had stable disease (n = 2 at 1 mg/kg q2w, and n = 1 each at 3 mg/kg q2w, 10 mg/kg q2w, 15 mg/kg q3w, and 20 mg/kg q4w). Conclusions: Initial results indicate no DLTs, 7 G2- and 1 G3-related AEs, and clinical activity for MEDI4736 in Japanese pts with advanced solid tumors. Based on these data, an expansion phase, including biliary tract cancer, SCCHN, and esophageal tumors, is underway. Clinical trial information: NCT01938612