Lymphovascular invasion as a prognostic value in small rectal neuroendocrine tumor treated by local excision: A systematic review and meta-analysis.

Because rectal neuroendocrine tumors (NETs) are usually small-sized despite of malignant potential, endoscopic resection techniques are recommended. It is unclear whether the lymphovascular invasion (LVI) in the endoscopic resected specimens of small rectal NETs should be indicated for completion surgery. We performed a systematic review and meta-analysis for the incidence of LVI in small rectal NETs (≤20 mm) treated by endoscopic resection and its prognostic impacts. We searched the relevant literature published before January 2019. A total of 21 publications including 1816 patients were enrolled. Overall prevalence of LVI in small rectal NETs was 21.8%. Immunohistochemical method significantly increased the detection rate of LVI up to 35.8% compared than H&E staining only (13.2%). Tumor size more than 5 mm was a risk factor for LVI in small rectal NET, whereas tumor grade did not influence the risk. The LVI in the endoscopic resected specimens was a risk factor for subsequent lymph node metastasis. Separately analyzed in detail, the vascular invasion had a stronger impact on lymph node metastasis than the lymphatic invasion. The prognosis of endoscopically treated rectal NET with LVI was excellent with only 0.3% of recurrence rate during the 5-year follow-up period. LVI is highly prevalent and a risk factor for lymph node metastasis in the small rectal NETs. Endoscopically treated small rectal NETs had excellent short-term prognoses despite of LVI. Immediate completion radical surgery is not absolutely necessary for the LVI-positive small rectal NETs. However, long-term follow-up is recommended for any delayed recurrence.