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290 Background: In patients with gastric cancer (GC), the most common double cancer is colorectal cancer (CRC). However, the meaning of screening colonoscopy has not been established. The aim of this retrospective study was to evaluate the useful of screening colonoscopy in preoperative patients with GC. Methods: This study included 689 patients who received screening colonoscopy before gastric surgery between 2012 and 2016. Multivariate analysis using logistic regression model was conducted to elucidate independent risk factors of CRC. Then, we investigated the clinicopathological factors for CRC. Results: Colorectal adenomas and CRC were observed in 315 patients (46%) and 37 patients (5.4%), respectively. The clinical T classification of the CRC were as follows; Tis: 24 patients (65%), T1: 8 patients (21%), T2: 2 patients (6%), and T3: 3 patients (8%). In multivariate analysis, male (OR 5.04, 95% C.I. 1.29-19.6, p = 0.020) was revealed as risk factor for affecting CRC. The treatments for CRC were as follows; EMR was performed in 27 patients, simultaneous resection with GC was performed in 9 patients, resection after gastrectomy was performed in 1 patient, respectively. Pathological stage of CRC was as follows; Stage 0: 24 patients, Stage I: 10 patients, and Stage IIA: 3 patients, respectively. As for the patients who underwent surgery for CRC, all of them received radical colectomy. No patient died for CRC who received colonoscopy before gastric surgery. Conclusions: Screening colonoscopy is useful for GC patients. Because most of the synchronous CRC were found early stage and curatively treated.

49 Background: Immune checkpoint inhibitors (ICPIs) have provided clinical benefit for various malignancies. A new attempt was recently made to combine PD-1/PD-L1 inhibitors and other ICPIs. In order to establish a new strategy for ICPI combination therapy, we must first understand the expression patterns of PD-L1 and other ICP molecules. To identify possible candidate agents for application in combination therapy with PD-1/PD-L1, we analyzed the expression patterns of ICP molecules in gastric cancer. Methods: Tumor samples were obtained from 278 patients who underwent gastrectomy for gastric cancer from 2014 to 2016, and a comprehensive gene expression analysis using a DNA microarray. We analyzed the TCGA dataset to identify the candidate ICP molecules in relation to PD-L1. The immune landscape was evaluated according to the expression patterns of known immune cell markers reported by Bindea et al. Results: Seven ICP molecules ( PD-L2, IDO1, CD80, ICOS, CTLA4, LAG3 and TIM3) were coexpressed with PD-L1 in the TCGA dataset. In our cohort, all of these molecules were also coexpressed (R > 0.5, P < 0.0001). Using a cluster analysis based on these gene expression profiles, patients were divided into Group A, characterized by the co-overexpression of PD-L1 and other ICP molecules, and Group B, characterized by the underexpression of PD-L1. In Group A, PD-L2 (R = 0.67) and IDO1 (R = 0.61) were particularly strongly associated with the PD-L1 expression. In Group B, elevated expressions of CTLA4 and ICOS were predominantly observed, and these expressions were strongly correlated with each other (R = 0.90). The tumor stage was significantly more advanced in Group B than in Group A (P = 0.02). Accordingly, Group A exhibited a better survival outcome than Group B. The immune landscape of Group A was particularly enriched for Th1, NK CD56dim and activated dendritic cells. Conclusions: PD-L1 and several immune checkpoint molecules tend to be coexpressed in gastric cancer. The combination of PD-L1/-L2 and IDO1 target agents may be a new strategy for treating gastric cancer with PD-L1 overexpression. In contrast, the underexpression of PD-L1 might be an indication for the use of CTLA4- and/or ICOS-directed therapies.

55 Background: We have previously reported the safety of robotic gastrectomy (RG) for clinical Stage IA or IB gastric cancer in single arm phase II studies. To date, a number of retrospective case control studies comparing RG and laparoscopic gastrectomy (LG) have been performed. However, since randomized controlled trials have never been conducted, no definitive conclusion demonstrating benefits of RG over LG has been demonstrated. In this study, we aimed to evaluate the safety of RG compared to LG using propensity score matching (PSM) methods. Methods: We retrospectively reviewed 766 consecutive patients who underwent either RG (n = 231) or LG (n = 535) for gastric cancer between January 2012 and December 2017. A 1:1 PSM was performed with the matched variables of age, sex, body mass index, performance status, clinical Stage, type of gastrectomy, and extent of lymphadenectomy. We compared short-term outcomes between the patients who underwent RG (RG group) and LG (LG group). Results: After PSM analysis, 231 patients were included in the RG group and 230 in the LG group. Intraoperative blood loss was similar between the groups. Operation time was significantly longer in the RG group (326 min vs. 281 min, P < 0.001). Significantly more lymph nodes were retrieved in the RG group (42 vs. 38.5, P = 0.031). Serum CRP level were significantly lower in the RG group in postoperative day 3 (9.0 mg/dL vs. 9.8 mg/dL, P = 0.049) and 6 (3.1 mg/dL vs. 3.7 mg/dL, P = 0.034), and drain amylase level in postoperative day 3 was also significantly lower in the RG group (612 U/L vs. 856 U/L, P < 0.001). Overall postoperative complication (Clavien–Dindo classification grade IIIA or greater) was similar between the groups (RG: 3.9% vs. LG: 5.6%, P = 0.656). However, pancreatic fistula tended to be less frequent in the RG group than in the LG group (0.4% vs. 2.2%, P = 0.122), although it did not reach statistically significant difference. Conclusions: Although RG takes longer operation time, it appears to be less invasive than LG with the possibility of decreased postoperative complications. To validate the results, randomized controlled trial should be performed.

27 Background: Although prolonged preoperative waiting period (PWP) for gastric cancer (GC) may influence the prognosis, the relationship between PWP and survival outcome has not been elucidated. The aim of this study is to identify the impact of PWP on survival in patients with clinical stage (cStage) II / III GC. Methods: A total of 483 patients who underwent surgery for cStage II / III GC according to Japanese classification of GC, 14th edition, between January 2002 and December 2012 were included. The patients who underwent endoscopic submucosal dissection or neoadjuvant chemotherapy, or who had multiple cancer, special histological types of tumor, or urgent symptoms were excluded. We defined PWP as the period from the date of endoscopy for initial diagnose to that of surgery. Patients were divided into two groups according to PWP; short waiting period group (SWPG, PWP ≤ 60 days, n = 357) and long waiting period group (LWPG, PWP > 60 days, n = 126). Survival outcomes were compared between the groups and multivariate analysis for overall survival (OS) was conducted to identify independent prognostic factors. Results: The median PWP was 49 (21-323) days. In LWPG, patients were significantly older (P = 0.001) and had more comorbidities (P = 0.042) than those in SWPG. Preoperative lymph node status was significantly lower in LWPG (P = 0.031), although there were no differences in tumor depth and cStage between the groups. There was no difference in OS between the groups (5-year OS, SWPG: 61.0%, LWPG: 63.2%, P = 0.612). Multivariate analysis for OS identified age, BMI, histological type, and cStage as independent prognostic factors. Conclusions: Preoperative waiting period appears to have no influence on survival in patients with cStage II / III GC.

653 Background: The impact of previous abdominal surgeries on the need for conversion to open surgery and on short-term outcomes during/after laparoscopic colorectal surgery was retrospectively investigated. This retrospective cohort study was conducted from May 2004 through October 2012. This study was conducted at Tokushima University Hospital and Ehime Prefectural Central Hospital. Methods: A total of 145 consecutive patients who had undergone laparoscopic resection of the sigmoid colon and upper rectum were classified as not having previous abdominal surgery (NPAS group, n = 123) or as having previous abdominal surgery (PAS group, n = 22). Short-term outcomes were assessed between the two groups. Results: The population of previous abdominal surgery consisted of 6 appendectomy, 3 gastrectomy for gastric ulcer, 2 nephrectomy, 2 peritonitis and 11 others (2 duplication). There were no significant differences in age, gender, BMI, tumor location, tumor size, Stage, operating time, blood loss and number of lymph node harvest between the two groups. The conversion to open surgery was performed in 1 patient (4.5%) in the PAS group and 6 patients (4.9%) in the NPAS group. The intraoperative inadvertent enterotomy occurred in 1 patient in the NPAS group. There was no difference in postoperative morbility between the two groups. In the NPAS group, anastomotic leakage was observed in 3 cases. Ileus was observed in one case in the NPAS and none in the PAS. Postoperative hospital stay was 14 days in the PAS group and 16 days in the NPAS group. Conclusions: Short-term outcomes following laparoscopic surgery for sigmoid colon and upper rectal cancer with previous abdominal surgery are acceptable.

643 Background: Safety and validity of performing laparoscopic surgery after preoperative lavege using the self-expandable metallic stent (SEMS) for left-sided obstructive colorectal cancer were examined. We evaluated the short-term outcome of SEMS insertion compared with laparoscopic surgery without SEMS. Methods: Patients with left-sided colorectal cancer treated by either laparoscopic surgery with stent placement (n = 8) or laparoscopic surgery only (n = 42) in our hospital between April, 2012 and January, 2013 were registered. Short-term outcomes were compared with the two groups about patient characteristics (sex, age, American Society of Anesthesiologists Physical Status, body mass index, prior abdominal surgery), pathological data of patients (tumor location, size of tumor , tumor differentiation, number of harvested lymph nodes, pTNM classification, UICC pathological stage), and operative and post operative results (procedures, conversion, operative time, blood loss, morbidity, solid food intake, postoperative hospital stay, total hospital stay). Results: Except for tumor size in the patient characteristic parameters, there were no statistically significant difference between the two groups. Conversion rate to laparotomy was higher in the stent group (2 versus 1, p = 0.013). There was no difference in operation time, blood loss and postoperative complications between the two groups. Conclusions: Although the long-term oncological result requires further investigation, laparoscopic surgery after self-expandable metallic stent is a safe and feasible treatment as a “brige to surgery” for left-sided obstructive colorectal cancer.