Different MiRNAs Related to Mutations or High Mitotic Indices Contribute to Rectal Neuroendocrine Tumors: A Pilot Study

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 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 mutations or high mitotic indices in rectal NETs, which may play a critical role in tumor behavior.