HE staining image of the tumor tissue. (A) The cystic spaces were lined by a columnar mucinous epithelium that presented papillary folding. Higher power view of columnar mucinous epithelium is displayed on the bottom-right corner. (B) There was a small number of stromal invasive features in the bottom of the solid part of this cystic tumor. (C) Near the carcinoma in situ, OGCs were distributed diffusely in the stroma of the cyst wall. (D) The tumor showed the invasion to the stomach across the serosal layer.