Treatment strategy for rectal carcinoids: A clinicopathological analysis of 229 cases at a single cancer institution

Background and Aim: A treatment strategy for tumors with only venous invasion and characteristics of small rectal carcinoids with metastasis have not been clearly documented. The present study aims to determine the risk factors for lymph node metastasis and to elucidate characteristics of small tumors with metastasis. Methods: We investigated a total of 229 patients with rectal carcinoids. The relationship between each clinicopathological variable and the presence of lymph node metastasis was evaluated. Results: Tumor size (larger than 10 mm), presence of central depression, depth of tumor invasion, lymphatic invasion, and venous invasion were significantly associated with the incidence of lymph node metastasis (P < 0.001). Multivariate analysis revealed that tumor size (odds ratio: 63.3, P < 0.001) and venous invasion (odds ratio: 40.9, P < 0.001) were independently predictive of lymph node metastasis. In 204 patients with small (no larger than 10 mm) tumors, 10 patients had lymph node metastasis. All 10 tumors had low proliferation values indicated by mitosis and Ki‐67 index. Multivariate analysis for the 204 patients revealed that only venous invasion was independently associated with metastasis (odds ratio: 40.1, P < 0.001). Five‐year disease free survival rates of the total patients with metastasis and without metastasis were 81.1% and 95.5%, respectively (P < 0.001, log‐rank test). Conclusions: Venous invasion as well as tumor size and lymphatic invasion indicates high malignant potential to metastasize to lymph node and would provide useful information in considering the addition of radical surgery. Postoperative pathological examinations of specimens obtained by local resection are very important to avoid underestimation.