Fig. 1Colonoscopic findings. (A) An approximately 1-cm yellowish round submucosal tumor was observed in the sigmoid colon. (B) Follow-up colonoscopy 1 year later showed that the submucosal mass increased in size to approximately 3 cm.
Fig. 2Endoscopic ultrasound findings. An approximately 1×1-cm heterogeneous hypoechoic tumor with well-demarcated border (arrows) was found on the submucosal layer.
Fig. 3Pathologic findings. (A) Gross findings after segmental colon resection revealed that the mass was well circumscribed and located at the submucosal and muscular layers with central infiltration of the serosa. Histologic examination showed (B) proliferation of large polygonal cells with abundant eosinophilic granular cytoplasm and vascular invasion of tumor cells (thick arrows) (H&E stain, ×200), (C) perinodal lymphatic invasion of tumor cells (thin arrows) (H&E stain, ×100), and (D) immunohistochemical positivity for S-100 protein (S-100 protein, ×40).