Rectal neuroendocrine tumors: Current advances in management, treatment, and surveillance

Abstract

Rectal neuroendocrine neoplasms (r-NENs) are considered among the most frequent digestive NENs, together with small bowel NENs. Their incidence has increased over the past few years, and this is probably due to the widespread use of endoscopic screening for colorectal cancer and the advanced endoscopic procedures available nowadays. According to the current European Neuroendocrine Tumor Society (ENETS) guidelines, well-differentiated r-NENs smaller than 10 mm should be endoscopically removed in view of their low risk of local and distant invasion. R-NENs larger than 20 mm are candidates for surgical resection because of their high risk of distant spreading and the involvement of the muscularis propria. There is an area of uncertainty regarding tumors between 10 and 20 mm, in which the metastatic risk is intermediate and the endoscopic treatment can be challenging. Once removed, the indications for surveillance are scarce and poorly codified by international guidelines, therefore in this paper, a possible algorithm is proposed.

Keywords: Rectal neuroendocrine tumors, Endoscopy, Endoscopic submucosal dissection, Resectable advanced disease, Systemic therapy

Core Tip: Rectal neuroendocrine neoplasms (r-NENs) represent 1%-2% of all rectal tumors, but an increasing incidence rate has been recently reported. Up to 90% of r-NENs are < 10 mm in size, confined to the submucosa, and well-differentiated, so that the endoscopic resection represents their gold-standard therapy. Advanced metastatic NENs are usually poorly differentiated G3 carcinomas treated with chemotherapy, except for rare G1-G2 neoplasms, which can be targeted with less aggressive systemic options. Locally advanced r-NENs invading submucosal layers, with a ≥ 10 mm diameter, but still without distant metastases, represent the real therapeutic challenge among rectal tumors.