Superficial Serrated Adenoma: A Rare Case of Sigmoid Polyp With Malignant Potential.

We present the case of a 68-year-old woman who underwent complete endoscopic resection of a superficial serrated adenoma (SuSA). Due to its rarity and limited case reports, SuSA is often misdiagnosed as a hyperplastic lesion without malignant potential, leading to missed diagnoses. A polypoid lesion was identified in the sigmoid colon during the initial endoscopic evaluation, where it was initially classified as a sessile serrated lesion (SSL). The subsequent endoscopic evaluation, using crystal violet staining, revealed a type IIIL pit pattern. Endoscopic mucosal resection (EMR) was performed, and histopathological analysis confirmed serrated glandular hyperplasia with mild atypia. Immunohistochemical staining showed cytokeratin 20 (CK20) expression predominantly in the upper layer, while Ki-67 and cellular myelocytomatosis oncogene (c-MYC) were distributed in the basal and intermediate layers. Beta-catenin positivity was observed in the cytoplasm of some nuclei, confirming the diagnosis of SuSA. This case underscores the importance of timely recognition and management of SuSA to prevent progression to more severe conditions.