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Recent studies suggest that miRNA may be involved in the development of rectal neuroendocrine tumors (NETs). We explored the frequency of clinicopathologically relevant mutations and miRNA expression in rectal NETs to examine molecular profiles related to prognosis and behavior. Twenty-four eligible specimens with endoscopically excised rectal NETs were selected. Next-generation sequencing and an miRNA expression assay were used to evaluate the expression profile relevant to common genetic mutations in rectal NETs. Kyoto Encyclopedia of Genes and Genomes analysis predicted that the possible target signaling pathways were correlated with dysregulated miRNAs. Nineteen rectal NETs harbored more than one mutation in the 24 cancer-related genes. Seven miRNAs (hsa-miR-769-5p, hsa-miR-221-3p, hsa-miR-34a-5p, hsa-miR-181c-5p, hsa-miR-1246, hsa-miR-324-5p, and hsa-miR-361-3p) were significantly down-regulated in tumors harboring the FBWX7 mutation. Unsupervised hierarchical clustering analysis showed that up-regulation of these seven miRNAs may result in high mitotic indices, indicating the role of miRNAs in tumor progression. Among the down-regulated miRNAs, hsa-miR-769-5p was strongly correlated with extracellular matrix-receptor interaction and lysine degradation. Among the clinicopathological factors, up-regulated hsa-miR-3934-5p was linked to an increased mitotic count. No change in miRNA expression was associated with a tumor size >1 cm, lymphovascular invasion, or Ki-67 index. In summary, we identified different miRNA signatures involved in FBXW7 mutations or high mitotic indices in rectal NETs, which may play a critical role in tumor behavior.

Rectal neuroendocrine tumors (NETs) are the most common gastrointestinal (GI) NETs with an uncertain malignant potential despite their small size. There are limited data about driver mutations in rectal NETs, which may explain the tumors' unexpected behavior or common histologic morphology with other GI-NETs. Here, we investigated the clinically and pathologically relevant mutations of rectal and nonrectal NETs and compared the frequency and clinical significance of detected mutations between them. We sequenced 84 primary GI-NETs (69 rectal, 7 gastric, 5 appendiceal, and 3 sigmoid colon NETs) and 3 metastatic GI-NETs using targeted next-generation sequencing. Twenty-one rectal NETs (30.4%) showed at least 1 mutation in 24 cancer-related genes; the most common mutations were TP53 (10.1%) and FBXW7 (7.2%), of which 73% were pathogenic/likely pathogenic mutations. TP53 (p.R337C and p.R213*), PTEN (p.W111*, p.Q214*), CDKN2A (p.W110*), FBXW7 (p.R465H), and AKT1 (p.R23Q) were repetitive mutations found exclusively in rectal NETs, whereas SMAD4 (p.R361C) and STK11 (p.D176N) were repetitive mutations found only in gastric NETs. PTEN (p.G129K), EGFR (p.E709K), and KIT (p.V555I) were shared mutations between rectal and appendiceal NETs, whereas SMAD4 (p.R361C), ALK (p.G1202R), VHL (p.Q132*), and IDH1 (p.R132H) were concurrently detected between rectal and gastric NETs. GI-NETs with higher histologic grades, lymphovascular invasion, or recurrence tended to have higher numbers of mutation variants than other tumors; however, there was no significant difference. In conclusion, rectal NETs commonly carried pathogenic/likely pathogenic mutations. Because most mutations were identified in nonhotspot positions, next-generation sequencing is useful in identifying potential drug targets in rectal NETs., (Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved.)

Mitotic counts in the World Health Organization (WHO) grading system have narrow cutoff values. True mitotic figures, however, are not always distinguishable from apoptotic bodies and darkly stained nuclei, complicating the ability of the WHO grading system to diagnose well-differentiated neuroendocrine tumors (NETs). The mitosis-specific marker phosphohistone H3 (PHH3) can identify true mitoses and grade tumors reliably. The aim of this study was to investigate the correspondence of tumor grades, as determined by PHH3 mitotic index (MI) and mitotic counts according to WHO criteria, and to determine the clinically relevant cutoffs of PHH3 MI in rectal and nonrectal gastrointestinal NETs. Mitotic counts correlated with both the Ki-67 labeling index and PHH3 MI, but the correlation with PHH3 MI was slightly higher. The PHH3 MI cutoff ≥4 correlated most closely with original WHO grades for both rectal NETs. A PHH3 MI cutoff ≥4, which could distinguish between G1 and G2 tumors, was associated with disease-free survival in patients with rectal NETs, whereas that cutoff value showed marginal significance for overall survival in patient with rectal NETs. In conclusion, the use of PHH3 ≥4 correlated most closely with original WHO grades.

Aim: To identify the frequency, clinicopathological risk factors, and prognostic significance of lymphovascular invasion (LVI) in endoscopically resected small rectal neuroendocrine tumors (NETs)., Methods: Between June 2005 and December 2015, 104 cases of endoscopically resected small (≤ 1 cm) rectal NET specimens at Hallym University Sacred Heart Hospital in Korea were retrospectively evaluated. We compared the detected rate of LVI in small rectal NET specimens by two methods: hematoxylin and eosin (H&E) and ancillary immunohistochemical staining (D2-40 and Elastica van Gieson); in addition, LVI detection rate difference between endoscopic procedures were also evaluated. Patient characteristics, prognosis and endoscopic resection results were reviewed by medical charts., Results: We observed LVI rates of 25.0% and 27.9% through H&E and ancillary immunohistochemical staining. The concordance rate between H&E and ancillary studies was 81.7% for detection of LVI, which showed statistically strong agreement between two methods (κ = 0.531, P < 0.001). Two endoscopic methods were studied, including endoscopic submucosal resection with a ligation device and endoscopic submucosal dissection, and no statistically significant difference in the LVI detection rate was detected between the two (26.3% and 26.8%, P = 0.955). LVI was associated with large tumor size (> 5 mm, P = 0.007), tumor grade 2 ( P = 0.006). Among those factors, tumor grade 2 was the only independent predictive factor for the presence of LVI (HR = 4.195, 95%CI: 1.321-12.692, P = 0.015). No recurrence was observed over 28.8 mo regardless of the presence of LVI., Conclusion: LVI may be present in a high percentage of small rectal NETs, which may not be associated with short-term prognosis., Competing Interests: Conflict-of-interest statement: The authors declare no conflict of interest.