Lymph Node Metastases do not Impact Survival in Follicular Variant Papillary Thyroid Cancer

IntroductionFollicular variant of papillary thyroid cancer (FVPTC) is the most common and fastest growing subtype of papillary thyroid cancer (PTC) with features of both PTC and follicular thyroid cancer (FTC). The purpose of this study was to determine the patient and tumor features associated with lymph node metastases (LNM) in FVPTC.MethodsThis was a retrospective review of adult (≥18) patients with histologically confirmed diagnoses of FVPTC within the SEER database between 1988 and 2009. LNM were defined by at least two lymph nodes with metastatic disease. To determine factors associated with LNM, we constructed a multivariate logistic regression model from significant variables (p < 0.05) identified on univariate analysis. Similarly, we used a Cox proportional hazards model to understand the relative importance of LNM in determining disease-specific mortality (DSM).ResultsOf the 20,357 cases of FVPTC with lymph node data available, 1,761 (8.7%) had LNM; 61.1% of these LNM were located in the central neck and 38.9% were in the lateral neck. Extrathyroidal extension (odds ratio [OR] 2.6, 95% confidence interval [CI] 2.2-3.0, p < 0.01) and multifocality (OR 3.0, 95% CI 2.5-3.6, p < 0.01) were the strongest predictors of LNM. Importantly, LNM did not independently predict DSM (p = 0.52). Tumor size >4 cm (hazards ratio [HR] 5.3, 95% CI 2.2-12.8, p < 0.01) and extrathyroidal extension (HR 8.2, 95% CI 3.0-22.0, p < 0.01) were the strongest predictors of DSM.ConclusionsLNM occur in less than 10% of patients with FVPTC but do not impact DSM. Instead, DSM in FVPTC is related to size and local invasion.