Objective  To explore the clinicopathological characteristics of lymph node-negative rectal neuroendocrine neoplasms (RNENs).

  Methods  We retrospectively analyzed and regularly followed up the clinical and pathological data of 83 patients with lymph node-negative rectal NENs treated at China-Japan Friendship Hospital between December 2012 to December 2019.

  Results  Among the 83 patients, 49 (59%) were male and 34 (41%) were female with an average age of (43.3±11.4) years. Of the patients, 61 (75.5%) were mainly treated for nonspecific symptoms, 75 (90.4%) had a single tumor with an average size of (0.8±0.7) cm, 80 (96.4%) showed tumor infiltration into the mucosal and submucosal layers, and 65 (78.3%) predominantly had tumors of pathological grade G1. The average Ki-67 index was (2.1±1.7)%, with 78 (94%) patients having stage I tumors. Twenty-nine (34.9%) patients showed CgA positivity on immunohistochemical analysis. As for treatment, 67 (80.7%) patients underwent endoscopic resection, and 16 (19.3%) patients underwent surgery. The median follow-up time was 24 (3-90) months, with a 100% 5-year survival rate and relapse in 2 (2.4%) patients. Tumor recurrence was significantly correlated with the Ki-67 positive index (P=0.025), and tumor infiltration depth was correlated with the tumor diameter (P=0.03). Kaplan-Meier analysis showed that different treatment mode and tumor grade on prognosis and recurrence was statistically significant (Log-rank P=0.031, 0.001).

  Conclusion  Lymph node-negative rectal neuroendocrine neoplasms with a diameter >1 cm infiltrate the muscularis propria relatively easily and those ≤ 1 cm may also infiltrate the muscularis propria. It is recommended that all patients undergo ultrasound enteroscope (EUS) to determine the treatment choice. Endoscopic resection is the main treatment for lymph node-negative rectal neuroendocrine neoplasms. Patients with a high Ki-67 index are relatively prone to relapse after treatment.