Predictors of Distant Metastasis in Patients with Medullary Thyroid Carcinoma

<b>Background/Objectives</b>: The presence of distant metastases is the main cause of death in medullary thyroid carcinoma (MTC). However, due to the rarity of this cancer, few studies have thoroughly analyzed the variables influencing the development of distant metastases. The objective of this study was to evaluate, in patients with MTC, the factors associated with the occurrence of synchronous and metachronous distant metastases. <b>Methods</b>: An analytical, observational, retrospective cohort study was conducted at a tertiary hospital. Patients with histologically confirmed MTC, both sporadic and familial (MEN2 syndrome), were included. The influence of epidemiological variables, heredity, complementary tests, surgical factors, histological features, staging, and disease progression was assessed. A univariate comparative analysis was first performed, followed by a multivariate analysis using logistic regression. <b>Results</b>: This study included 146 patients, of whom 75% (<i>n</i> = 109) had familial MTC. Lymph node involvement at diagnosis was observed in 36% (<i>n</i> = 52). During follow-up, distant metastases developed in 14% (<i>n</i> = 21) of patients, including five cases present at the time of diagnosis. The median follow-up was 214 months (IQR 106-289). The presence of distant metastases was associated with an increased risk of mortality. Factors associated with distant metastases included age, calcitonin level, hereditary status, lymph node involvement, and overall stage. In multivariate analysis, the lymph node ratio (LNR) remained the only significant predictor (OR 29.124). <b>Conclusions</b>: Several variables were related to the presence of distant metastases. Among them, the LNR emerged as the independent predictor of both synchronous and metachronous distant metastases.