Gastric Extent of Tumor Predicts Peritoneal Metastasis in Siewert II Adenocarcinoma

Background: Whereas current guidelines recommend staging laparoscopy for most patients with potentially resectable gastric cancer, such a recommendation for patients with adenocarcinoma of the gastroesophageal junction (AEG) is lacking. This study sought to identify baseline clinicopathologic characteristics associated with peritoneal metastasis (PM) among patients with Siewert II AEG. Methods: Trimodality therapy–eligible patients with Siewert II AEG (2000-2015, single institution) were retrospectively identified. A composite PM outcome was defined as follows: (1) PM at staging laparoscopy; (2) PM diagnosed during neoadjuvant chemoradiation; or (3) PM ≤6 months postoperatively. Logistic regression was used to identify features associated with PM; bootstrapped analysis (Youden J) identified the distal tumor extension that best discriminated the composite outcome. Results: Of 188 patients, a composite PM outcome was observed in 26 of 188 (13.8%); 12 of 26 had positive staging laparoscopy, 10 of 26 experienced PM during chemoradiation, and 4 of 26 had PM ≤6 months postoperatively. Tumor extension below the GEJ was greater in patients with PM (median, 4.0 cm [interquartile range, 3.0-5.0] vs 3.0 cm [interquartile range, 2.0-3.0]; P < .001). All patients with PM had cT3 to cT4 tumors. Among patients with cT3 to cT4 tumors (n = 168 of 188; 89.4%), distal tumor extent (odds ratio, 1.67/cm; 95% CI, 1.23-2.28; P = .001) was independently associated with increased odds of PM. Gastric tumor extension ≥4 cm remained independently associated with PM (OR, 5.14; 95% CI, 2.11-12.53; P < .001) after adjustment for signet ring cell status. Conclusions: Distal tumor extent beyond the GEJ is independently associated with increased odds of PM in patients with Siewert II AEG. Patients with extensive gastric involvement should therefore be considered for staging laparoscopy before trimodality therapy.