Significance of the Surgical Treatment with Lymph Node Dissection for Neuroendocrine Tumors of Thymus

SIMPLE SUMMARY: Neuroendocrine tumors of the thymus (NETTs) are rare and have a poor prognosis. Complete resection would be the best method to achieve a radical cure, although a standardized treatment method has not been established. Additionally, no standard criteria have been developed to determine the necessity of tumor resection alone or total thymectomy, and the same is true for lymph node dissection. We reviewed 40 patients who underwent surgical resection, including lymph node dissection and biopsy. The overall survival (OS) rate was better in the resected cases but with no significant differences in histological grade and pathological stage. NETTs frequently develop lymph node metastasis; thus, lymph node dissection seems necessary to achieve complete resection, especially for local control. Recurrence frequently occurs, but complete resection and multidisciplinary treatment would be effective because of the relatively good OS. ABSTRACT: Background: Neuroendocrine tumors of a thymus (NETTs) are rare, accounting for approximately 2–5% of all thymic epithelial tumors, and have a poor prognosis due to frequent lymph nodes or distant metastasis. Methods: We retrospectively reviewed the clinicopathological background and outcomes of 40 patients who underwent resection or surgical biopsy with histologically diagnosed NETTs from 1986 to 2022. Results: The most common pathological type was atypical carcinoid. Surgical resection was performed in 35 patients, with lymph node dissection in 33 and surgical biopsy in five. The overall survival (OS) rate for all patients was 81.4% and 52.3% at 5 and 10 years, respectively. The 2-year survival rate was 20% for the biopsy group, which was significantly worse than that of the resected group (p < 0.001). The relapse-free survival rates were 61.7% and 37.6% at 5 and 10 years, respectively, in 34 patients with complete resection. The univariate analysis revealed better the OS rate in the resected cases but with no significant differences between histological grade, lymph node metastasis, tumor size, or Ki67 index. Conclusions: Surgical complete resection is considered to improve prognosis regardless of histologic type. NETTs frequently develop lymph node metastasis, thus, lymph node dissection seems necessary for complete resection.