title: Risk of malignancy according to sub-classification of the atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) category in the Bethesda system for reporting thyroid cytopathology.
abstract: OBJECTIVE
  According to the Bethesda System for Reporting Thyroid Cytopathology, atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) is a heterogeneous category that includes cases with architectural and/or nuclear atypia insufficient to warrant classification as malignant neoplasms. The ambiguous and descriptive characteristics of the AUS/FLUS category mean that the impact of the present guidelines on repeat fine needle aspiration (FNA) is unclear. The present study reclassified AUS/FLUS cases into four sub-categories and then correlated them with histological or cytological follow-up data to clarify the risk of malignancy.
  
  
  METHODS
  Ninety-four cases of AUS/FLUS with available follow-up data were reviewed and assigned to one of four sub-categories: (i) AUS-N (nuclear atypia); (ii) AUS-A (architectural atypia); (iii) AUS-O (predominant oncocytic changes); and (iv) AUS-N/A (both nuclear and architectural atypia). The four sub-categories were correlated with subsequent histological or cytological follow-up data, including core needle biopsy, resection, or repeat FNA.
  
  
  RESULTS
  Malignancy was identified in 34 of 94 cases (36.2%). The upper limit estimate for malignancy was 43.6%, and the lower limit estimate was speculated as 9.8%. The malignancy rate was highest in cases within the AUS-N sub-category (65.8%, range 16.6%-78.1%).
  
  
  CONCLUSIONS
  The present study suggests that cases in the AUS/FLUS category have a higher risk of malignancy than previously thought. Because of the heterogeneous nature of the AUS/FLUS category, further sub-classification might be more effective in achieving appropriate risk stratification and better clinical management.
authors.affiliation: Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: S J
authors.initials: SJ
authors.lastname: Kim
authors.affiliation: Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: J
authors.initials: J
authors.lastname: Roh
authors.affiliation: Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: J H
authors.initials: JH
authors.lastname: Baek
authors.affiliation: Department of Surgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: S J
authors.initials: SJ
authors.lastname: Hong
authors.affiliation: Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Y K
authors.initials: YK
authors.lastname: Shong
authors.affiliation: Department of Internal Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: W B
authors.initials: WB
authors.lastname: Kim
authors.affiliation: Department of Pathology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: D E
authors.initials: DE
authors.lastname: Song
mesh_terms: D000328:Adult; D000368:Aged; D044963:Biopsy, Fine-Needle; D003581:Cytodiagnosis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D013961:Thyroid Gland / Q000473:pathology*; D013964:Thyroid Neoplasms / Q000145:classification / Q000175:diagnosis* / Q000473:pathology; D016606:Thyroid Nodule / Q000145:classification / Q000175:diagnosis* / Q000473:pathology
keywords: atypia of undetermined significance; fine needle aspiration; follicular lesion of undetermined significance; risk of malignancy; sub-category; thyroid cytopathology