The frequency of early colorectal cancer derived from sessile serrated adenoma/polyps among 1858 serrated polyps from a single institution.

BACKGROUND AND AIM: Sessile serrated adenoma/polyps (SSAPs) are suspected to have a high malignant potential, although few reports have evaluated the incidence of carcinomas derived from SSAPs using the new classification for serrated polyps (SPs). The aim of study was to compare the frequency of cancer coexisting with the various SP subtypes including mixed polyps (MIXs) and conventional adenomas (CADs). METHODS: A total of 18,667 CADs were identified between April 2005 and December 2011, and 1858 SPs (re-classified as SSAP, hyperplastic polyp (HP), traditional serrated adenoma (TSA), or MIX) were removed via snare polypectomy, endoscopic mucosal resection, or endoscopic sub-mucosal dissection. RESULTS: Among 1160 HP lesions, 1 (0.1%) coexisting sub-mucosal invasive carcinoma (T1) was detected. Among 430 SSAP lesions, 3 (0.7%) high-grade dysplasia (HGD/Tis) and 1 (0.2%) T1 were detected. All of the lesions were detected in the proximal colon, with a mean tumor diameter of 18 mm (SD 9 mm). Among 212 TSA lesions, 3 (1%) HGD/Tis were detected but no T1 cancer. Among 56 MIX lesions, 9 (16%) HGD/Tis and 1 (2%) T1 cancers were detected, and among 18,677 CAD lesions, 964 (5%) HGD/Tis and 166 (1%) T1 cancers were identified. CONCLUSIONS: Among the resected lesions that were detected during endoscopic examination, a smaller proportion (1%) of SSAPs harbored HGD or coexisting cancer, compared to CAD or MIX lesions. Therefore, more attention should be paid to accurately identifying lesions endoscopically for intentional resection and the surveillance of each SP subtype.

Cancer emerging from the recurrence of sessile serrated adenoma/polyp resected endoscopically 5 years ago.

Since the serrated neoplastic pathway has been regarded as an important pathway of colorectal carcinogenesis, few reports have been published on clinical cases of cancer derived from sessile serrated adenoma/polyp, especially on recurrence after resected sessile serrated adenoma/polyp. An elderly woman underwent endoscopic mucosal resection of a flat elevated lesion, 30 mm in diameter, in the ascending colon; the histopathological diagnosis at that time was a hyperplastic polyp, now known as sessile serrated adenoma/polyp. Five years later, cancer due to the malignant transformation of the sessile serrated adenoma/polyp was detected at the same site. The endoscopic diagnosis was a deep invasive carcinoma with a remnant sessile serrated adenoma/polyp component. The carcinoma was surgically removed, and the pathological diagnosis was an adenocarcinoma with sessile serrated adenoma/polyp, which invaded the muscularis propria. The surgically removed lesion did not have a B-RAF mutation in either the sessile serrated adenoma/polyp or the carcinoma; moreover, the initial endoscopically resected lesion also did not have a B-RAF mutation. Immunohistochemistry confirmed negative MLH1 protein expression in only the cancer cells. Lynch syndrome was not detected on genomic examination. The lesion was considered to be a cancer derived from sessile serrated adenoma/polyp recurrence after endoscopic resection, because both the surgically and endoscopically resected lesions were detected at the same location and had similar pathological characteristics, with a serrated structure and low-grade atypia. Furthermore, both lesions had a rare diagnosis of a sessile serrated adenoma/polyp without B-RAF mutation. This report highlights the need for the follow-up colonoscopy after endoscopic resection and rethinking our resection procedures to improve treatment.