[Clinicopathological analysis of superior mediastinal lymph node metastases in medullary thyroid carcinoma]

Objective: To investigate the clinicopathological characteristics of superior mediastinal lymph node metastases (sMLNM) in medullary thyroid carcinoma (MTC). Methods: This retrospective analysis enrolled the patients who were treated for sMLNM of MTC in our hospital from May 2012 to January 2021. All patients were suspected of sMLNM due to preoperative imaging. According to the pathological results, the patients were divided into two groups named sMLNM group and the negative superior-mediastinal-lymph-node group. We collected and analyzed the clinical features, pathological features, pre- and post-operative calcitonin (Ctn), and carcinoembryonic antigen (CEA) levels of the two groups. Logistic regression analysis was used to analyze risk factors, and receiver operation characteristic (ROC) curves were drawn to determine the optimal cut-off values of preoperative Ctn and preoperative CEA for predicting sMLNM. Results: Among the 94 patients, 69 cases were in the sMLNM group and 25 cases were in the non-SMLNM group. Preoperative Ctn level (P=0.003), preoperative CEA level (P=0.010), distant metastasis (P=0.022), extracapsular lymph node invasion (P=0.013), the number of central lymph node metastases (P=0.002) were related to sMLNM, but the multivariate analysis did not find any independent risk factors. The optimal threshold for predicting sMLNM by pre-operative Ctn is 1500 pg/ml and AUC is 0.759 (95% CI: 0.646, 0.872). The sensitivity, specificity, positive predictive value, and negative predictive value of diagnosis are 61.2%, 77.3%, 89.1%, 39.5%, respectively. In patients who underwent mediastinal lymph node dissection through transsternal approach, the metastatic possibility of different levels from high to low were level 2R (82.3%, 28/34), level 2L (58.8%, 20/34), level 4R (58.8%, 20/34), level 3 (23.5%, 8/34), level 4L (11.8%, 4/34). Postoperative complications occurred in 41 cases (43.6%), and there was no perioperative death in all cases. 14.8% (12/81) of the patients achieved biochemical complete response (Ctn≤12 pg/ml) one month after surgery, 5 of these patients were in sMLNM group. Conclusions: For patients who have highly suspicious sMLNM through imaging, combining with preoperative Ctn diagnosis can improve the accuracy of diagnosis, especially for patients with preoperative Ctn over 1 500 pg/ml. The superior mediastinal lymph node dissection for the primary sternotomy should include at least the superior mediastinal levels 2-4 to avoid residual lesions. The strategy of surgery needs to be cautiously performed. Although the probability of biochemical cure in sMLNM cases is low, nearly 40% of patients can still benefit from the operation at the biochemical level.