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Gastric cancer with gastric outlet obstruction (GOO) is generally found at an advanced stage and with an unfavorable prognosis. This study was performed to examine the prevalence of radiologically occult peritoneal carcinomatosis in GOO and determine the optimal treatment strategy.This single-center study was a retrospective review of the clinical data of 186 patients with locally advanced gastric cancer at the distal stomach who underwent surgery from 2008 to 2016. These patients were divided into two groups according to the presence or absence of GOO due to cancer progression: With GOO (n=71) and without GOO (n=115).The incidence of peritoneal carcinomatosis [with macroscopic peritoneal deposits (P1)/positive peritoneal cytology (CY1)] detected at laparotomy/laparoscopy was significantly higher in the group with GOO than in the group without (32.4% vs. 9.6%, p0.01). The R0 resection rate was lower in the group with GOO (62.0% vs. 87.0%, p0.01). The 5-year overall survival rate was also lower in the group with GOO (43.9% vs. 68.5%, p0.01). However, in the subset of patients who underwent R0 surgery, the 5-year rates were similar for the two groups (67.4% vs. 73.1%, p=0.91). The multivariable analysis showed that a type 3 tumor appearance (odds ratio=3.66) and presence of GOO (odds ratio=2.87) were predictors of peritoneal carcinomatosis.The prevalence of radiologically occult peritoneal carcinomatosis in gastric cancer with GOO exceeded 30%. Staging laparoscopy (gastrojejunal bypass, if needed) should be performed to determine the optimal treatment plan.

Postoperative intra-abdominal infection is known to adversely affect survival outcomes in patients with gastric cancer; however, previous reports have investigated this complication only in open surgery. This adverse effect is expected to be weakened by less invasive surgery, such as a laparoscopic approach, by way of maintaining immune function.This study included 1223 patients with gastric cancer who underwent open (n = 439) or laparoscopic (n = 784) curative surgery between 2010 and 2015. For each approach, patients were divided into two groups based on presence or absence of postoperative intra-abdominal infection of Clavien-Dindo grade II or higher (C-group and NC-group, respectively). Survival outcomes were compared in propensity-matched cohorts to evaluate the impact of the complication.The incidences of Clavien-Dindo ≥ grade II postoperative intra-abdominal infectious complications were 9.7% (43/439) in open surgery and 9.8% (70/714) in laparoscopic surgery. After propensity score matching, 86 patients in open surgery and 138 in laparoscopic surgery were extracted for analysis. The 5-year overall survival rate in the open C-group (n = 43) was worse than that in the open NC-group (n = 43) but with no significant difference (70.9% vs. 82.8%, log-rank P = 0.18). The 5-year overall survival rates were equivalent between the laparoscopic C-group (n = 69) and the laparoscopic NC-group (n = 69) (90.5% vs. 90.4%, log-rank P = 0.99).In general, postoperative intra-abdominal infection adversely affects survival outcomes; however, its impact may be weakened by less invasive surgery. Further evaluation using larger datasets is necessary before reaching definitive conclusions.

Background Robotic gastrectomy (RG) is being increasingly performed globally; it is considered an evolved type of conventional laparoscopic surgery with excellent dexterity and precision, but higher costs and longer operation time. Thus, there is a need to identify the benefits from RG and its specific candidates. Methods This retrospective study analyzed data from a prospectively collected clinical database at our center. Data of patients with primary gastric cancer undergoing either robotic or laparoscopic radical gastrectomy from June 2014 to June 2020 were reviewed. Surgical outcomes were compared between the two groups, and multivariable analyses were performed to elucidate the relevant factors for postoperative complications in several subgroups. Results A total of 1172 patients were divided into those who underwent RG (n = 152) and those who underwent laparoscopic gastrectomy (LG) (n = 1020). Baseline characteristics were similar in the two groups, except the RG group included more patients undergoing total/proximal gastrectomy (TG/PG) and patients at clinical stage III. Compared with the LG group, the RG group had lower incidences of postoperative complications ≥ Clavien-Dindo grade III (2/152 (1.3%) versus 72/1020 (7.1%); P = 0.004), and intraabdominal complications ≥ grade II (6/152 (3.9%) versus 119/1020 (11.7%); P = 0.004). Multivariable analysis revealed that RG was a significant relevant factor for reducing overall postoperative complications (≥ grade III) (odds ratio (OR) 0.16, P = 0.013), and intraabdominal complications (≥ grade II) (OR 0.29, P = 0.002). Subgroup analyses demonstrated that this tendency was enhanced in patients undergoing TG/PG (OR 0.29, P = 0.021) or at clinical stage II/III (OR 0.10, P = 0.027). Conclusions RG reduces the incidence of postoperative complications compared with conventional LG and this tendency may be enhanced in technically complicated procedures with demanding anastomosis or D2 lymphadenectomy. Patients requiring such procedures would most benefit from RG.

416 Background: Platinum-based definitive chemoradiotherapy (dCRT) is the standard treatment for patients (pts) with unresectable locally advanced esophageal squamous cell carcinoma (ESCC), invading the aorta, vertebral body, or trachea. However, complete response (CR) rates are low (11–25%), with a median overall survival (OS) of 9–10 months. We previously reported atezolizumab following dCRT indicated promising 42.1% of confirmed CR (cCR) rate and 65.8% of 12-months OS (Bando H, et al., ESMO Congress 2022 ). Methods: We investigated predictive biomarkers for cCR in this multicenter phase II study. PD-L1 tumor proportion score (TPS) was examined with VENTANA PD-L1. Immunological phenotypes of tumor microenvironments were assessed with multiplex immunohistochemistry (mIHC) and multi-color flow cytometry (FCM). Cancer gene aberrations and gene expression were investigated with whole exome and whole transcriptome sequencing (WES/WTS), respectively. Results: In 35 pts with an evaluable PD-L1 TPS, the cCR rates of +CD8+PD-1+ T cells and CD3+CD8-FOXP3+ T cells prior to CRT in tumor tissue were significantly correlated with cCR and non-cCR, respectively (both are P+CD8+ T cells prior to CRT, after CRT, and after atezolizumab were significantly correlated with cCR (P+FOXP3highCD45RA-CD4+ regulatory T cells (Treg cells) after CRT were significantly correlated with non-cCR (P+CD8+ T cells prior to CRT may be a predictive biomarker for cCR of CRT followed by atezolizumab, and that several driver gene abnormalities, cancer intrinsic signatures and tumor-infiltrating Treg cells are associated with treatment resistance. These findings could enable subsequent biomarker-selected clinical trials and lead to the development of novel cancer immunotherapeutic strategies. Clinical trial information: UMIN000034373 .

252 Background: The standard treatment for patients with unresectable locally advanced esophageal squamous cell carcinoma (ESCC) is platinum-based definitive chemoradiotherapy (dCRT). Previous clinical trials have indicated a clinical complete response (cCR) rate of 11%-25% and median overall survival (OS) of 9-10 months. The cCR rate is strongly correlated with good prognosis, however the predictive factors have not been elucidated. Methods: In this multi-institutional retrospective study, we evaluated the efficacy and safety of dCRT in patients with unresectable locally advanced ESCC. “Unresectable” was defined as the primary lesion (T4b) invading adjacent structures such as the aorta, vertebral body, and trachea, or the regional and/or supraclavicular lymph nodes (LNT4b) invading unresectable adjacent structures. cCR was determined by both computed tomography and endoscopy based on the Response Evaluation Criteria in Solid Tumors (version 1.1) with modifications and Japanese Classification of Esophageal Cancer (11th edition), respectively. Results: A total of 175 patients who started dCRT between January 2013 to March 2020, were included in this study. The overall median age was 68 (31-86). A total of 95 (54%) patients had a performance status of 0. Of these, 124 (71%) patients had T4b and 81 (46%) had LNT4b. The clinically involved site were as follows: thoracic aorta (22%), tracheobronchial tree (73%), and others (14%). The median tumor length was 6 (2-22) cm. 56 (32%) patients were tube-fed owing to obstructive tumors. 165 (96%) patients completed at least one cycle of chemotherapy with 60 Gy of radiation. Further, 84 (48%) patients received consolidation chemotherapy following dCRT. The confirmed cCR rate was 24% (42/175). At a median follow-up interval of 20 months, the 2-year OS and progression-free survival (PFS) rates of cCR cases vs. non-cCR cases were 90% vs. 31% (log-rank p < 0.001) and 59% vs. 2% (log-rank p < 0.001), respectively. Multivariate analysis of the clinicopathological factors contributing to cCR revealed that a tumor length of≥6 cm (OR, 0.4; 95% CI, 0.2–0.9 p = 0.03) was the only a significant predictive factor. The primary adverse events of grade 3 or above were esophagitis (32%), pneumonitis (13%), fistula formation (10%), febrile neutropenia (9%), and dyspnea (6%). Among 22 patients who originally presented with fistula formation, fistula disappeared in 14 (64%), including 3 cCR cases. Two (1%) sudden deaths secondary to severe hemorrhage and suspected aortic fistula were observed during the treatment period. Conclusions: dCRT is feasible for patients with unresectable locally advanced ESCC. The cCR rate of dCRT is consistent with that reported in previous clinical trials, and favorable OS and PFS rates were observed in patients with cCR. Tumor length was observed to be a significant predictive factor of cCR. Research Sponsor: None.

While there have been numerous reports about colovesical fistulas and ruptured intestinal diverticula, there have been far fewer reports about vesicointestinal fistulas caused by Meckel’s diverticula. Most Meckel’s diverticula are asymptomatic. Furthermore, they seldom cause vesicointestinal fistulas, and the associated complications are non-specific. Thus, their preoperative diagnosis is difficult. We experienced a case in which a vesicointestinal fistula was caused by a Meckel’s diverticulum and was treated with laparoscopic surgery. A 46-year-old male was referred to our hospital after exhibiting hematuria. Cystoscopy revealed a fistula between the small intestine and bladder. Contrast-enhanced computed tomography and magnetic resonance imaging showed a diverticulum in the ileum and a fistula between the ileum and bladder, which passed through the diverticulum. A Meckel’s diverticulum was suspected. We conducted a laparoscopic operation. We dissected the Meckel’s diverticulum with an automatic suturing device and removed it together with part of the ileum. The patient’s postoperative course was good. We experienced a case in which a vesicointestinal fistula was caused by a Meckel’s diverticulum and was successfully treated with laparoscopic surgery. In selected cases of Meckel’s diverticulum, the dissection of the diverticulum with an automatic suturing device is appropriate.