title: Lymph node metastases do not impact survival in follicular variant papillary thyroid cancer.
abstract: BACKGROUND
  Follicular 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.
  
  
  METHODS
  This 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).
  
  
  RESULTS
  Of 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.
  
  
  CONCLUSIONS
  LNM 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.
authors.affiliation: Section of Endocrine Surgery, Department of Surgery, University of Wisconsin, K3/738 Clinical Science Center, 600 Highland Avenue, Madison, WI, 53792, USA, schneiderd@surgery.wisc.edu.
authors.forename: David F
authors.initials: DF
authors.lastname: Schneider
authors.forename: Dawn
authors.initials: D
authors.lastname: Elfenbein
authors.forename: Ricardo V
authors.initials: RV
authors.lastname: Lloyd
authors.forename: Herbert
authors.initials: H
authors.lastname: Chen
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Sippel
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000401:mortality* / Q000556:secondary / Q000601:surgery; D000328:Adult; D002291:Carcinoma, Papillary / Q000401:mortality* / Q000556:secondary / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008207:Lymphatic Metastasis; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D012189:Retrospective Studies; D018426:SEER Program; D015996:Survival Rate; D013964:Thyroid Neoplasms / Q000401:mortality* / Q000473:pathology / Q000601:surgery
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