Supplementary Material for: Long-term outcomes of endoscopic submucosal dissection for special type of esophageal cancer

Introduction: Esophageal cancers other than two types, squamous cell carcinoma (SCC) and adenocarcinoma, are commonly referred to as special type of esophageal cancer (STEC). Studies on STECs have been limited because of its low prevalence. Therefore, we aimed to clarify the clinicopathological findings and the long-term outcomes of STECs that were managed with ESD. Methods: We reviewed 713 patients with 1089 lesions who underwent ESD for primary esophageal cancer except Barrett’s esophageal cancer. Patients were classified into the SCC group and the STEC group, respectively. Their clinicopathological findings and long-term outcomes including diseases specific survival (DSS) were collected and examined. Results: A total of 19 consecutive patients (1.7 %) were diagnosed with STEC. Nine patients were diagnosed with basaloid carcinoma, 6 with adenosquamous carcinoma, 2 with mucoepidermoid carcinoma, 2 with salivary duct-type carcinoma, and 1 with neuroendocrine cell carcinoma. There was significantly more pT1b esophageal cancer (47.4% vs. 11.0%, p<0.01) and lymphovascular invasion (31.6% vs. 10.2%, p=0.011) in the STEC group. Metastatic relapse and disease-specific mortality were significantly higher in the STEC group (both 15.8% vs. 1.2%, p<0.01), and the STEC group had shorter DSS with 5-year DSS rates of 90.9%. In a subgroup analysis of patients with pT1a esophageal cancer, the 5-year DSS rate was shorter in the STEC group (p<0.01). In the multivariate analysis, STEC (HR=0.24) and tumor depth (HR=12.60) were the factors associated with DSS. Discussion/Conclusion: STECs are suggested to have high malignant potential and to be an independent negative prognostic factor for DSS.