title: Follicular variant of papillary thyroid carcinoma is a unique clinical entity: a population-based study of 10,740 cases.
abstract: BACKGROUND
  Follicular variant of papillary thyroid carcinoma (FV-PTC) has been increasingly diagnosed in recent years. However, little is known about its clinical behavior. The purpose of this study was to determine the disease characteristics of FV-PTC, and to compare it with classical papillary thyroid carcinoma (C-PTC) and follicular thyroid carcinoma (FTC).
  
  
  METHODS
  All cases of C-PTC, FV-PTC, and FTC larger than 1 cm in the Surveillance, Epidemiology and End Results (SEER) Cancer Database from 1988 to 2007 were identified. Tumor behavior and patient survival were compared among these three groups. Different risk factors for disease-specific mortality in each group were evaluated by multivariate analysis.
  
  
  RESULTS
  More than 36,000 surgical cases were identified, including 21,796 C-PTCs, 10,740 FV-PTCs, and 3958 FTCs. Extrathyroidal extension and lymph-node metastases were more common in FV-PTC than in FTC, but significantly less common than in C-PTC (p<0.0001). Distant metastasis rates were present in 2% of patients with FV-PTC, in 1% with C-PTC, and in 4% with FTC (p<0.0001). The 10-year disease-specific survival for patients with FV-PTC was 98%, similar to C-PTC (97%) but better than FTC (94%, p<0.0001). Being over the age of 45 years remained a strong risk factor for disease-specific mortality in both FV-PTC and C-PTC, while the presence of extrathyroidal extension and distant metastases were stronger predictors of disease-specific mortality in FV-PTC than in C-PTC.
  
  
  CONCLUSIONS
  FV-PTC is a common variant of PTC. Its clinical behavior is unique and represents an intermediate entity with clinical features that are between C-PTC and FTC. Interestingly, despite the variations in clinical behavior, the long-term outcome of these patients remains excellent and similar to C-PTC.
authors.affiliation: Section of Endocrine Surgery, Department of Surgery, University of Wisconsin School of Medicine and Public Health , Madison, Wisconsin.
authors.forename: Xiao-Min
authors.initials: XM
authors.lastname: Yu
authors.forename: David F
authors.initials: DF
authors.lastname: Schneider
authors.forename: Glen
authors.initials: G
authors.lastname: Leverson
authors.forename: Herbert
authors.initials: H
authors.lastname: Chen
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Sippel
mesh_terms: D018263:Adenocarcinoma, Follicular / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D000328:Adult; D000368:Aged; D002277:Carcinoma / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D002291:Carcinoma, Papillary / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D018265:Carcinoma, Papillary, Follicular / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D015331:Cohort Studies; D003131:Combined Modality Therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011379:Prognosis; D011877:Radionuclide Imaging; D012189:Retrospective Studies; D018426:SEER Program; D016019:Survival Analysis; D000077273:Thyroid Cancer, Papillary; D013961:Thyroid Gland / Q000473:pathology* / Q000601:surgery; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D047368:Tumor Burden; D014481:United States