Open versus minimally invasive surgery for large type 3 and type 4 gastric cancer: A multicenter retrospective study from high-volume centers in Japan.

383 Background: The optimal surgical approach for large type 3 and type 4 gastric cancers remains controversial. The objective of this study was to evaluate the safety and feasibility of minimally invasive surgery (MIS) such as laparoscopic and robotic approaches compared with open surgery for large type 3 and type 4 gastric cancer. Methods: This study included patients with large type 3 and type 4 gastric cancer who underwent open surgery or MIS between January 1, 2020, and December 31, 2022 at 63 high-volume centers in Japan. To compare the short-term outcomes and survival between the two approaches, inverse probability weighting (IPW) and stabilized average treatment effect weights based on each patient’s propensity score was applied. The following variables were included for propensity score estimation: age, sex, body mass index, American Society of Anesthesiologists physical status, clinical stage, preoperative chemotherapy, macroscopic type (large type 3/type 4), primary tumor location, tumor circumferential extent, esophageal invasion, splenic hilar dissection, and omentectomy. Results: A total of 1,013 patients who met the eligibility criteria were collected in this study. There were 505 patients with large type 3 gastric cancer and 508 patients with type 4 gastric cancer. Open surgery and MIS were performed in 653and 360 patients (laparoscopic surgery in 205 and robotic surgery in 155), respectively. Compared with open surgery, MIS resulted in a significantly longer operative time (334 vs. 282 min; P