Distant lymph node metastasis in differentiated thyroid cancer: A population-based cohort study.

Background: Cervical lymph node metastasis (LNM) is the most common clinical event in patients with differentiated thyroid cancer (DTC). However, the incidence, pattern, treatment, and prognosis of distant LNM are yet to be reported.

Methods: DTC patients with distant LNM were identified from the Surveillance, Epidemiology, and End Results (SEER) database between 2016 and 2020. Multivariate models and propensity score matching (PSM) were used to account for the effects of covariates. The Kaplan-Meier method was used to evaluate the overall survival (OS) and cancer-specific survival (CSS). A nomogram was established to predict the probability of distant LNM in DTC patients, with calibration and Receiver Operating Characteristic (ROC) curves utilized to validate the nomogram's accuracy.

Results: Of the 42,339 DTC patients screened, 100 (0.24 %) patients presented with distant LNM. Risk factors including age, sex, T stage, N stage, bone metastasis, brain metastasis, and lung metastasis were included in the nomogram to predict the probability of distant LNM. The calibration curve of the nomogram was close to the ideal diagonal line and the area under the curve (AUC) of the ROC curve is 0.953. Distant LNM showed a worse prognosis after adjusting for confounders compared with non-distant LNM (P < 0.05). Remarkably, radioactive iodine (RAI) therapy did not improve the OS and CSS in DTC patients with distant LNM in the overall or PSM cohort.

Conclusions: Distant LNM presents as a comparatively rare but grave condition with a substantial negative impact on prognosis in patients with DTC. Identified risk factors of distant LNM are older age, male, advanced T stage and N stage, bone metastasis, brain metastasis, and lung metastasis. Remarkably, the current RAI therapy does not appear to significantly improve the survival outcome of DTC patients with distant LNM.