Lymph node metastasis in thymic malignancies: A Chinese multicenter prospective observational study.

OBJECTIVES

To study the incidence and pattern of lymph node metastases in thymic malignancies.

METHODS

This multicenter prospective observational trial with intentional lymph node dissection was carried out by the Chinese Alliance for Research in Thymomas (ChART). Data on patients with thymic tumors without pretreatment were collected prospectively. Results from this prospective study were then compared with those from a previously reported ChART retrospective study.

RESULTS

Among 275 patients, metastasis was detected in 41 nodes (3.04%) in 15 patients (5.5%). The rate of lymph node metastasis was 2.1% (5/238) in patients with thymomas, 25% (6/24) in those with thymic carcinomas, and 50% (4/8) in those with neuroendocrine tumors (P < .001). The rate of lymph node metastasis in category T1 to T4 tumors was 2.7% (6/222) in T1, 7.7% (1/13) in T2, 18.4% (7/38) in T3, and 50% (1/2) in T4 (P < .001). Nodal involvement was significantly higher compared with the ChART retrospective study (5.5% vs 2.2%; P = .002), although the 2 groups were comparable in terms of tumor stage and histology. Metastasis was found in N1 nodes in 13 patients (86.7%) and in N2 nodes in 8 patients (53.3%); 6 patients (40%) had simultaneous N1/N2 diseases and 6 (40%) had multistation involvement. Based on World Health Organization histological classification and Union for International Cancer Control T category, patients were divided into a low-risk group (1/192; 0.5%) with T1-2 and type A-B2 diseases and a high-risk group (14/83; 16.9%) of category T3 and above or histology B3 and above tumors for nodal metastasis (P < .001). On multivariate analysis, type B3/thymic carcinoma/neuroendocrine tumors, category T3 or above, and N2 dissection predicted a greater likelihood of finding nodal metastasis.

CONCLUSIONS

Lymph node involvement in thymic malignancies is more common than previously recognized, especially in tumors with aggressive histology and advanced T category. Intentional lymph node dissection increases the detection of nodal involvement and improves accuracy of staging. In selected high-risk patients, systemic dissection of both N1and N2 nodes should be considered for accurate tumor staging.