4114 Background: We conducted a phase II study to evaluate the efficacy and safety of perioperative S-1 + docetaxel (DS) in locally advanced gastric cancer (LAGC), and to investigate the association between CYP2A6 genotypes and treatment outcomes. Methods: Eligibility criteria included 18-70 yrs, PS 0-1, measurable lesion(s), and LAGC (clinical stage III-IV (M0) by Japanese staging system). Pts were given each 3 cycles of pre- and post-operative chemotherapy (S-1 40 mg/m2 bid on D1-14, docetaxel 35 mg/m2iv on D1, 8 q 3 wks), and underwent surgery (≥D2). Results: From Oct 2006 to June 2008, 44 pts entered into the study, and 43 pts were eligible. Median age=53 yrs (range, 33-69); PS 0/1=2/41; M/F=29/14; and stage IIIA/IIIB/IV (M0)=20/18/5. All 43 eligible pts completed preoperative DS and 40 pts (93%) completed postoperative DS. The most common G3/4 toxicities during pre- and post-operative DS were neutropenia (28% vs. 65%), stomatitis (19% vs. 5%), and abdominal pain (5% vs. 18%). The clinical response rate was 74.4% (95% CI, 61.4-87.4%) with 1 CR (2.3%) and 31 (72.1%) PRs. R0 resection rate was 97.7%, major pathologic response rate was 48.8% with 1 CR, and pathologic stage was 0/1/2/3/4 (%) = 2.3/44.2/20.9/20.9/11.6. With a median follow-up of 66.6 months, 3-yr PFS and 5-yr OS was 62.8% and 69.6%, respectively. Survival differed according to clinical response, clinical downstaging, and CYP2A6 genotypes (Table). Pts with two CYP2A6 variant alleles (V/V) had higher Cmax (27.7±4.6 vs. 20.3±1.2; p=0.045) and AUCinf (220.4±43.1 vs. 172.5±12.5; p=0.187) of tegafur, and lower Cmax (1.4±0.2 vs. 1.8±0.1; p=0.178) and AUCinf (8.4±1.2 vs. 9.7±0.5; p=0.308) of 5-FU than those with no or one variant allele (W/W or W/V). Conclusions: DS is active with a manageable toxicity profile in the perioperative setting in pts with LAGC. CYP2A6 genotype may be predictive of efficacy (S-1 and docetaxel was provided by JEIL Pharm. Co., Ltd. and sanofi-aventis Korea Co., Ltd., respectively). Clinical trial information: NCT00587145. [Table: see text]