Circulating MicroRNAs in Small Bowel Neuroendocrine Tumors – a potential tool for diagnosis and assessment of effectiveness of surgical resection

Objective: To discover serum-based microRNA (miRNA) biomarkers for small bowel neuroendocrine tumors (SBNET) to help guide clinical decisions. Background: MiRNAs are small non-coding RNA molecules implicated in the initiation and progression of many cancers. MiRNAs are remarkably stable in bodily fluids, and can potentially be translated into clinically useful biomarkers. Novel biomarkers are needed in SBNET to determine disease aggressiveness, select patients for treatment, detect early recurrence and monitor response. Methods: This study was performed in 3 stages (discovery, validation and a prospective, longitudinal assessment). Discovery comprised of global profiling of 376 miRNA in sera from SBNET patients (n=11) vs. healthy controls (HC; n=3). Up-regulated miRNAs were subsequently validated in additional SBNET (n=33) and HC sera (n=14); and then longitudinally after SBNET resection (n=12), with serial serum sampling (pre-operatively day 0; post-operatively at 1 week, 1 month and 12 months). Results: Four serum miRNAs (miR-125b-5p, -362-5p, -425-5p and -500a-5p) were significantly up-regulated in SBNET (P<0.05; fold-change >2) based on multiple normalization strategies, and were validated by RT-qPCR. This combination was able to differentiate SBNET from HC with an AUC of 0.951. Longitudinal assessment revealed that miR-125b-5p returned towards HC levels at 1 month post-operatively in patients without disease, whilst remaining up-regulated in those with residual disease (RSD). This was also true at 12 months post-operatively. In addition, miR-362-5p appeared up-regulated at 12 months in RSD and recurrent disease (RCD). Conclusions: Our study represents the largest global profiling of serum miRNAs in SBNET patients, and the first to evaluate ongoing serum miRNA expression changes after surgical resection. Serum miR-125b-5p and miR-362-5p have potential to be used to detect RSD/RCD.