Serrated polyps of the colon and rectum (hyperplastic polyps, sessile serrated adenomas, traditional serrated adenomas, and mixed polyps)—proposal for diagnostic criteria

Abstract

Until recently, two major types of colorectal epithelial polyps were distinguished: the adenoma and the hyperplastic polyp. While adenomas-because of their cytological atypia-were recognized as the precursor lesions for colorectal carcinoma, hyperplastic polyps were perceived as harmless lesions without any potential for malignant progression mainly because hyperplastic polyps are missing cytological atypia. Meanwhile, it is recognized that the lesions, formerly classified as hyperplastic, represent a heterogeneous group of polyps with characteristic serrated morphology some of which exhibit a significant risk of neoplastic progression. These serrated lesions show characteristic epigenetic alterations not commonly seen in colorectal adenomas and progress to colorectal carcinoma via the so-called serrated pathway (CpG-island-methylation-phenotype pathway). This group of polyps is comprised not only of hyperplastic polyps, but also of sessile serrated adenomas, traditional serrated adenomas and mixed polyps, showing serrated and "classical" adenomatous features. Diagnostic criteria and nomenclature for these lesions are not uniform and, therefore, somewhat confusing. In a consensus conference of the Working Group of Gastroenterological Pathology of the German Society of Pathology, standardization of nomenclature and diagnostic criteria as well as recommendations for clinical management of these serrated polyps were formulated and are presented herein.

Impact of reassessment of colonic hyperplastic polyps by expert GI pathologists

“…They could also be missed more frequently, since they are mostly flat lesions and located in the right colon. Histological criteria have been developed on the basis of morphological changes and marker expressions [2,15]. The malignant potential of SSA has been regarded as substantial by some groups [23], but no consensus exists about both their occurrence and overall cancer risk in a broad community setting.…”

“…Table 1 Microscopic criteria for diagnosis of SSA according to the German Society of Pathology [15] • Hyperserration, serration in the lower third of the crypts with and without branching of the crypts • T-or L-shaped crypts above the muscularis mucosae Secondary outcomes & There is a likelihood of a shortening of recommended follow-up intervals on a per-patient basis, namely, shortening from 10 years (based on a diagnosis of HP only) to either 3 or 5-10 years based on the presence of adenomas. For this analysis, SSA were treated like adenomas with respect to follow-up recommendations [16,17], although this practice might not be regarded as finally established.…”

“…The distinction between SSA and HP, however, may be difficult, and previous studies have also reported poor to fair interobserver agreement rates for histopathological diagnosis of SSA versus HP, with kappa values ranging from 0.16 to 0.38 [11,13,14]. For these reasons, diagnostic criteria for SSA have been recently refined by several expert panels and consensus conferences [2,15], in the hope of arriving at a more uniform and reproducible histopathological diagnosis.…”

Serrated colorectal polyps in inflammatory bowel disease

“…The rates of BRAF and KRAS mutations in serrated polyps negative for dysplasia and serrated polyps positive for low-grade dysplasia in our study closely resembles the rates reported in sporadic sessile serrated adenoma/polyps and traditional serrated adenomas, respectively. 4,5,26 This observation, in conjunction with their corresponding sex and anatomical site disparities, suggests that biologic parallels exist with sporadic sessile serrated adenoma/polyps and traditional serrated adenomas, despite the origin of at least 97% of our serrated polyps within chronically diseased inflammatory bowel disease mucosa. Although supervening cytologic dysplasia has been reported in up to 15% of sporadic sessile serrated adenoma/polyps, 27,28 we did not encounter this phenomenon in our study, where serrated polyps with cytologic dysplasia histologically resembled sporadic traditional serrated adenomas.…”

Traditional serrated adenoma has two pathways of neoplastic progression that are distinct from the sessile serrated pathway of colorectal carcinogenesis

“…1 However, the biological significance of these two morphological patterns is still unknown. Although some pathologists diagnose tumors with combined features as mixed hyperplastic/adenomatous polyps or mixed polyps with a description of the constituent components, 17,18 mixed polyps have also been reported to share similar molecular changes and implicate morphological progression to malignancy. 13,19 Jass et al 13 reported that traditional serrated adenoma with dysplastic epithelium resembling conventional adenoma displayed a high frequency of KRAS mutation, whereas Kim et al 7 linked this traditional serrated adenoma to a lower frequency of BRAF mutation.…”