Endoscopic features of isolated and traditional serrated adenoma-associated superficially serrated adenomas of the colorectum

Traditional serrated adenoma with superficially serrated adenoma: A case treated with endoscopic submucosal dissection with detailed endoscopic observation and pathological study

A new subtype of serrated lesions, superficially serrated adenoma (SuSA), has been proposed as a lesion that histopathologically exhibits the morphological features of both conventional adenomas and serrated lesions and is difficult to classify as either one. SuSA has been elucidated to be a precursor lesion of KRAS-type traditional serrated adenoma. It has also been reported that SuSA may have malignant potential. We report a case treated with endoscopic submucosal dissection and detailed observation. Endoscopy revealed a raised lesion with a two-tier raised appearance in the sigmoid colon: a tall pinecone-like reddish structure and flattened whitish elevation on white light imaging. Magnifying narrow-band imaging revealed conspicuous blood vessels in the pinecone-like structure and slightly dilated reticular vessels in the flattened area. Crystal violet staining showed that the pinecone-like structure had a type IV_H pit pattern and the flattened area had a stellate to slightly elongated type III_H pit pattern diagnosed based on Kudo's classification and other pit pattern classification systems. Ki67-positive cells were distributed in the basal and middle layers of the gland in the flattened elevated area. Genetic analysis results were positive for KRAS mutation and negative for BRAF mutation. Histopathological examination revealed a traditional serrated adenoma in the pinecone-like structure and SuSA in the adjacent flattened elevated area.

Sessile serrated lesions with dysplasia: is it possible to nip them in the bud?

The serrated neoplasia pathway constitutes an "alternative route" to colorectal cancer (CRC), and sessile serrated lesions with dysplasia (SSLDs) are an intermediate step between sessile serrated lesions (SSLs) and invasive CRC in this pathway. While SSLs show indolent growth before becoming dysplastic (> 10-15 years), SSLDs are considered to rapidly progress to either immunogenic microsatellite instable-high (MSI-H) CRC (presumably 75% of cases) or mesenchymal microsatellite stable (MSS) CRC. Their flat shapes and the relatively short window of this intermediate state make it difficult to detect and diagnose SSLDs; thus, these lesions are potent precursors of post-colonoscopy/interval cancers. Confusing terminology and the lack of longitudinal observation data of serrated polyps have hampered the accumulation of knowledge about SSLDs; however, a growing body of evidence has started to clarify their characteristics and biology. Together with recent efforts to incorporate terminology, histological studies of SSLDs have identified distinct dysplastic patterns and revealed alterations in the tumor microenvironment (TME). Molecular studies at the single-cell level have identified distinct gene alterations in both the epithelium and the TME. Mouse serrated tumor models have demonstrated the importance of TME in disease progression. Advances in colonoscopy provide clues to distinguish pre-malignant from non-malignant-SSLs. Recent progress in all aspects of the field has enhanced our understanding of the biology of SSLDs. The aim of this review article was to assess the current knowledge of SSLDs and highlight their clinical implications.