Abstract
This report describes a 53-year-old woman admitted for evaluation of a space-occupying lesion in the ascending colon detected one year earlier and recent right lower quadrant pain. Initial colonoscopy revealed a 2.0 × 2.0 cm submucosal elevated lesion with surface ulceration near the ileocecal valve. Biopsy showed inflammatory mucosa with abundant mucin but no malignancy, and CT revealed no definite abnormalities. One year later, the lesion enlarged to 3.5 × 3.0 cm with increased ulceration. Endoscopic ultrasound (EUS) demonstrated a hypoechoic submucosal mass, and endoscopic submucosal dissection (ESD) was performed. During ESD, a jelly-like substance raised suspicion of a mucinous neoplasm, leading to laparoscopic resection of the ileocecal region and ascending colon. Pathology confirmed mucinous adenocarcinoma originating from the submucosal layer. This rare presentation differs from typical colorectal cancers that arise from the epithelial layer. The combined use of EUS, ESD, and laparoscopic surgery facilitated accurate diagnosis and effective treatment.