Background: AZD7762, a potent Chk1/Chk2 inhibitor, has been shown to enhance the antitumor activity of gemcitabine in xenograft models (Zabludoff SD et al. Mol Cancer Ther 2008;7:2955–66). Methods: This open-label dose-escalation study evaluated the safety, pharmacokinetics (PK), and preliminary efficacy (RECIST) of AZD7762 alone and in combination with gemcitabine in Japanese patients (pts) with advanced solid tumors (NCT00937664). Pts received AZD7762 iv alone on days 1 and 8 of a 14-day cycle (Cycle 0), followed by AZD7762 plus gemcitabine 1000 mg/m² on days 1 and 8 of 21-day cycles, in sequential ascending AZD7762 dose cohorts. Results: 20 pts (mean age 60 years) received AZD7762 at doses of 6 (n=3), 9 (3), 21 (6), and 30 mg (8). The most common primary tumor site was lung (n=14). All pts had received ≥1 prior chemotherapy and 18 had metastatic disease. Dose-limiting toxicities (DLTs) occurred in two of six evaluable pts (both 30 mg cohort): one, grade 3 (CTCAE, v3.0) elevated troponin T (Cycle 0; AZD7762 monotherapy); one, neutropenia, thrombocytopenia, and elevated AST and ALT (Cycle 1; combination therapy). Thus, the 30 mg dose was regarded as non-tolerable. DLTs resolved following treatment discontinuation. The most frequently reported adverse events (AEs) in Cycle 0 (AZD7762 monotherapy) were bradycardia (50%), hypertension (25%) and fatigue (15%). Overall, the most common AEs were bradycardia (55%), neutropenia (45%), and hypertension, fatigue, and rash (30% each). AEs grade ≥3 were reported in 11 pts, the most common being neutropenia (45%) and leukopenia (25%). No pt died due to an AE. AZD7762 exposure (C_max, AUC) increased in an approximately linear manner. Gemcitabine did not appear to affect AZD7762 PK. Arithmetic mean t_½ and geometric mean CL of AZD7762 across the dose groups were 16.1–19.4 h and 22.0–32.7 L/h, respectively during the monotherapy cycle, and 15.6–18.3 h and 21.1–24.4 L/h, respectively in combination with gemcitabine. There were no objective responses; five pts (all lung cancer) had stable disease. Conclusions: The maximum tolerated dose of AZD7762 in combinationwith gemcitabine 1000 mg/m² was determined as 21 mg in Japanese pts.