[Case of a 5mm Rectal Neuroendocrine Tumor(G1)with Lymph Node Metastasis].

Screening colorectal endoscopy revealed a 5mm rectal neuroendocrine tumor(NET: G1)in a 72-year-old man. Endoscopic mucosal resection(EMR)was performed, and the histopathological examination demonstrated lymphatic and vessel invasion with a possible positive vertical margin. Therefore, we performed laparoscopic low anterior resection, lymphadenectomy, and ileostomy as additional surgical resections. No residual tumor was found in the specimen, but 3 metastatic lymph nodes were identified. The rate of lymph node metastasis in rectal NETs of diameter<10mm is low, and additional surgery can reduce the patient's quality of life affected due to impaired anorectal function. However, in the Japanese guidelines for NET, additional surgery is adopted in cases with high-risk factors for lymph node metastasis. Therefore, it is necessary to select between additional surgery and careful follow-upfor rectal NETs of diameter<10mm with high-risk factors because of possible lymph node metastasis.