Lymph Node Involvement and the Surgical Treatment of Thymic Epithelial and Neuroendocrine Carcinoma

Thymic epithelial and neuroendocrine carcinomas are rare malignancies, and only a few prognosticators are defined. Surgery is the mainstay of treatment, and complete resection contributes to superior outcome. Systematic lymph node dissection is not routinely performed in thymic malignancies. The aim of this study was to assess the impact of histologically confirmed lymph node metastases on the outcome after thymectomy.

We identified 53 patients with thymic epithelial or neuroendocrine carcinomas who underwent surgical resection at our center between 1999 and 2016. The clinical follow-up was retrospectively collected, and the impact of clinicopathologic factors on overall survival was analyzed.

Ninety-one percent of the patients were treated taking a multimodal approach. Median overall survival was 11.3 years. Lymph node metastases were identified in 16 patients (30.2%; 11 pN1 and 5 pN2). Lymph node metastasis was associated with inferior overall survival (hazard ratio [HR] 3.03, 95% confidence interval [CI]: 1.03 to 8.87, p = 0.044). Masaoka-Koga stage (4 versus 1 to 3) was another significant prognosticator (HR 7.01, 95% CI: 2.52 to 19.50, p = 0.0002). Organ metastases were present in 18 patients at the time of thymectomy and were associated with inferior outcome (HR 5.8, 95% CI: 2.04 to 16.79, p = 0.001).

This retrospective, single-center analysis demonstrates a high rate of lymph node metastasis in resectable thymic neuroendocrine tumors or carcinomas. Positive lymph nodes are associated with an inferior outcome. Prospective studies are warranted to explore whether this outcome can be improved by systematic lymphadenectomy and adjuvant therapies. Nevertheless, lymphadenectomy provides optimal staging and should be a routine part of surgery for patients with thymic malignancies.