BACKGROUND: The surgery of adenocarcinoma of the esophagogastric junction (AEG) is a complex procedure that increases postoperative morbidity compared to distal gastric cancer. In this study, we included thoracic anatomical parameters of patients for the first time to investigate their impact on the postoperative outcomes of transabdominal gastrectomy for Siewert type II/III AEG. METHODS: All patients with Siewert type II or III AEG of our institution who underwent transabdominal proximal or total gastrectomy from January 2015 to December 2022 were included in this study. We measured thoracic anatomical parameters on the level of the lower edge of the sternum using preoperative computer tomography. The anteroposterior diameter of the thorax was measured as the distance from the posterior edge of the sternum to the anterior edge of the spine, while the transverse diameter was the maximum distance between the ribs on both sides. Patients' data and postoperative details were retrospectively collected. Correlation between thoracic anatomical parameters with postoperative complications were analyzed. RESULTS: Overall, 647 patients were eligible for this study. The incidence of postoperative complications was 28.1%, with postoperative pulmonary complications occurring in 24.7%. In multivariate analysis, anteroposterior thoracic diameter >
10.2 cm was an independent risk factor for postoperative complications (OR = 1.891, 95% CI: 1.137-3.146, p = 0.014), transverse thoracic diameter >
23.3 cm was an independent risk factor for postoperative pulmonary complications (OR = 2.243, 95% CI: 1.234-4.079, p = 0.004). In open group, transverse thoracic diameter over 23.3 cm correlated independently with postoperative complications (OR = 2.451, 95% CI: 1.219-4.927, p = 0.012) and postoperative pulmonary complications (OR = 2.988, 95% CI: 1.407-6.347, p = 0.004). However, this correction was not significant in laparoscopy-assisted group. CONCLUSIONS: Thoracic size is an independent risk factor affecting the postoperative outcomes of transabdominal gastrectomy for Siewert type II and III AEG. Patients with larger thoracic cage are at a higher risk of postoperative complications, particularly pulmonary complications. For those patients, laparoscopic surgery may be a viable option.