Clinicopathologic and Endosonographic Characteristics of Colon Subepithelial Tumors Discovered Incidentally

Background/Aims: Colonoscopy is commonly used for colorectal cancer screening; therefore, the detection of colon subepithelial tumors (SETs) has also increased. Several research studies have been undertaken to diagnose and treat stomach and rectal SETs. The purpose of this study was to determine a diagnostic point for colon SETs by comparing histological findings with the endoscopic characteristics of colon SETs discovered by chance. Methods: A total 194 patients underwent an endoscopic ultrasound (EUS) for suspicious colon SETs during a colonoscopy from May 2014 to December 2021. A total of 105 colon SETs, which were histologically diagnosed, were finally included. Fisher’s exact test was used to determine the factors associated with malignant SETs. Results: Colon SETs were predominantly present in the right colon (n = 73, 69.5%), particularly in the transverse colon (n = 32, 30.5%). The majority were smaller than 10 mm (n = 88, 83.8%), and they had hard consistencies (n = 84, 80%) and exhibited no surface changes (n = 96, 91.4%). Most of them were found in the submucosal layers (n = 54, 51.4%) and had a hypoechoic pattern (n = 56, 53.3%) in the EUS. Of the histologically confirmed cases, only three (3/105, 2.9%) were malignant. Most benign lesions were lipomas, suspected parasitic infections, or lesions caused by various inflammatory reactions, including fibrous/fibrocalcific lesions and necrotic nodules. All soft lesions were benign. Two of the three malignant lesions were adenocarcinomas, and the other was lymphoma. For the malignant SETs, there was a statistically significant alteration in the surface of the tumors (p < 0.001), and they were located where the muscularis mucosa layer was included (p = 0.008). The potential malignant SETs, granular cell tumors, and neuroendocrine tumors (NETs) had similar features, such as yellowish hypoechoic masses. Colon NETs were only found in the rectosigmoid junction. Parasitic infections and lesions, resulting in various inflammatory reactions, were observed as pale and hard SETs and mostly revealed as mixed echogenic masses located in the muscularis mucosa, submucosa, or multi-layers in the EUS. Conclusion: This study showed that small colon SETs were mostly benign lesions. Despite its rarity, pathological confirmation is crucial in cases where the SET has surface changes and has been located in a position where the muscularis mucosa layer was included on the EUS, due to the risk of malignancy.