LAUSR

Abstract Objectives Extension of adenocarcinoma of the esophagogastric junction under the squamous epithelium may lead to errors when determining lateral margins. However, the characteristics of subsquamous extension are unclear. Herein, we evaluated the prevalence and characteristics of subsquamous extension of adenocarcinoma of the esophagogastric junction and the diagnostic performance of endoscopy for this condition. Methods Eighty-nine consecutive patients with superficial adenocarcinoma of the esophagogastric junction who underwent endoscopic or surgical resection at a tertiary cancer center between January 2010 and December 2017 were retrospectively evaluated. Endoscopic subsquamous extension was defined as a submucosal tumor-like elevation covered by squamous epithelium and/or a brownish area with abnormal microvessels on the squamous epithelium observed using narrow-band imaging. The diagnostic performance of endoscopy for subsquamous extension was evaluated using histological subsquamous extension as gold standard. Results Thirty-nine patients (44%) had histological subsquamous extension. Proton pump inhibitor use was significantly associated with histological subsquamous extension [odds ratio: 4.65; 95% confidence interval (CI): 1.77–12.2]. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of endoscopic subsquamous extension were 56% (95% CI: 40–72%), 96% (86–99%), 92% (73–99%), 74% (62–84%) and 79% (69–87%), respectively. The median length difference between histological and endoscopic subsquamous extension was 2 mm (range: −6 to 9 mm). Conclusions The sensitivity of endoscopic diagnosis of subsquamous extension was unsatisfactory. The endoscopic length of subsquamous extension tended to be underestimated. An oral safety margin of one centimeter is reasonable during endoscopic resection of adenocarcinoma of the esophagogastric junction. IMPACT STATEMENT  This study will contribute significantly to the literature because this is the first study to determine the difference between the lengths of subsquamous extension detected endoscopically and histologically. This study determines the prevalence of subsquamous extension and identifies characteristics associated with subsquamous extension. An understanding of the risk of subsquamous extension is important when choosing a treatment strategy and planning the resection margins in patients with adenocarcinoma of the esophagogastric junction. This study provides patients with subsquamous extension characteristics and suggests a method for accurately diagnosing this condition.