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Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance

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The Bethesda System for Reporting Thyroid Cytopathology

Abstract

Atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS) was introduced in 2008 as one of three “indeterminate” (not clearly benign or malignant) diagnostic reporting categories for thyroid fine needle aspirations. The two terms are alternatives and equally acceptable; it is not recommended that both be used by a laboratory to imply distinctly different interpretations. Each of the indeterminate categories has an elevated risk of malignancy (ROM) compared to a benign aspirate. The AUS/FLUS category is reserved for cases with atypia, cytologic and/or architectural in nature, that is insufficient for either of the other two indeterminate categories. Of the three indeterminate categories, AUS/FLUS has the lowest ROM, meriting its distinction from the other two. Follow-up studies since the introduction of the AUS/FLUS category indicate a ROM that is higher than predicted initially (~10–30% rather than ~5–15%). Furthermore, the risk differs according to the nature of the atypia prompting the AUS/FLUS interpretation. Specifically, AUS/FLUS with cytologic atypia raising concern for papillary carcinoma has a higher ROM than AUS/FLUS associated with architectural atypia alone or Hürthle cells. The introduction of noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) terminology in 2016 will decrease the overall ROM for AUS/FLUS. The clinical approach to a nodule with an initial AUS/FLUS interpretation is a repeat FNA or molecular testing, although patient preference and clinical risk factors may also impact management.

Based on published experience with AUS/FLUS in clinical practice, this update:

  1. (a)

    Details the appropriate use of the AUS/FLUS diagnostic terminology

  2. (b)

    Describes subclassification for the most common AUS/FLUS patterns to improve communication between cytologists and clinicians and to allow further refinement of the category as the impact of new information and entities (i.e., NIFTP) are further defined

  3. (c)

    Updates the management of AUS/FLUS, including the use of molecular testing

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Author information

Authors and Affiliations

  1. Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, 75 Francis Street, Boston, MA, 02115, USA

    Jeffrey F. Krane

  2. Department of Pathology, Northwestern University, Feinberg School of Medicine and Northwestern Medicine, Chicago, IL, USA

    Ritu Nayar

  3. Department of Pathology, Baptist Hospital, Miami, FL, USA

    Andrew A. Renshaw

Authors
  1. Jeffrey F. Krane
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  2. Ritu Nayar
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  3. Andrew A. Renshaw
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Corresponding author

Correspondence to Jeffrey F. Krane .

Editor information

Editors and Affiliations

  1. Department of Pathology, The Johns Hopkins Hospital/The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA

    Syed Z. Ali

  2. Department of Pathology, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, USA

    Edmund S. Cibas

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Krane, J.F., Nayar, R., Renshaw, A.A. (2018). Atypia of Undetermined Significance/Follicular Lesion of Undetermined Significance. In: Ali, S., Cibas, E. (eds) The Bethesda System for Reporting Thyroid Cytopathology. Springer, Cham. https://doi.org/10.1007/978-3-319-60570-8_4

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  • DOI: https://doi.org/10.1007/978-3-319-60570-8_4

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  • Online ISBN: 978-3-319-60570-8

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