Endoscopic and Clinicopathological Features of a Colorectal Mucin-Rich Variant of Traditional Serrated Adenoma.

Abstract

Introduction: The mucin-rich variant of traditional serrated adenoma (MR-TSA), pathologically defined by the presence of goblet cells comprising over 50% of the lesion compared to the absorptive epithelial eosinophilic cytoplasm, was recently introduced as one morphological variants of traditional serrated adenoma (TSA). This study aimed to characterize the endoscopic and clinicopathological characteristics of MR-TSAs.

Methods: Lesions pathologically diagnosed as TSAs at our hospital between 2011 and 2023 were reviewed. We analyzed the endoscopic and clinicopathological features of 49 MR-TSAs and 236 conventional TSAs (C-TSAs). Furthermore, immunohistochemical and genetic analyses were performed to ensure that there were no discrepancies with our previous study.

Results: MR-TSAs, like C-TSAs, were often located in the sigmoid colon and rectum, with no significant difference in lesion size. Macroscopically, MR-TSAs frequently appeared as type 0-Is with a weak reddish color and had a mucous cap, less often exhibiting a pinecone-like or coral-shaped appearance compared to C-TSAs (p < 0.001). Magnifying endoscopy showed expanded crypt openings in 80% of MR-TSAs (p < 0.001). Both groups had similar IIIH and IVH pit patterns. Immunohistochemical analysis revealed that MUC5AC was expressed more frequently in MR-TSAs than in C-TSAs. Additionally, genetic analysis showed that MR-TSAs more frequently harbored the BRAF mutation than C-TSAs (p < 0.001), whereas MR-TSAs less frequently harbored the KRAS mutation than C-TSAs (p = 0.047).

Conclusion: MR-TSAs, frequently harboring the BRAF but not KRAS mutation, exhibited several distinct endoscopic findings, including a sessile morphology, lack of pinecone-like or coral-like appearance, weak reddish color, and mucous cap.