Background: The relationship between extent of cervical lymphadenectomy along with the number of involved lymph nodes (LNs) removed and overall survival has not been well documented in patients with medullary thyroid carcinoma (MTC). This study investigates whether the overall number of LNs removed and the number of metastatic LNs are independent prognostic factors for overall survival. Methods: Data from patients with MTC in the Surveillance, Epidemiology, and End Results (SEER) registry database were examined. After categorizing the study population based on the number of overall LNs examined and the number of metastatic LNs, survival estimates were compared. The total number of examined LNs and their histopathological status were analyzed for their prognostic value in estimating overall survival. Results: 593 patients were included in this study. Those with all negative LNs had the best overall survival; those with LNs examined and at least one positive LN had worst overall survival (p<0.0001). The total number of examined LNs for both groups with negative and positive LNs was not associated with improved survival outcome (p = 0.41). In node-positive patients, each additional positive LN was significantly associated with an increase in overall mortality [hazard ratio (HR) = 1.05, 95% confidence interval (CI) = 1.02-1.08]. Conclusions: Cervical LN metastases conferred an independent risk for worse survival rate in MTC. Cervical lymphadenectomy is important for staging and regional disease control, however the extent of lymph node dissection, the overall number of lymph nodes removed along with removal of an increased number of involved lymph nodes do not confer a survival advantage. Future prospective studies are needed.
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