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      Malignancy Risk in 18F-FDG-Avid Thyroid Incidentalomas: Controversies and Limitations

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      , MD 1 , , MS 2 , , MD 3
      Journal of the Endocrine Society
      Oxford University Press

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          Abstract

          Introduction: The prevalence of malignancy in thyroid incidentalomas (TI) discovered on 18F-FDG-PET or PET/CT varies between 0% and 63.6%. The pooled malignancy rate according to three systematic reviews is 33-35%. The 2015 American Thyroid Association (ATA) guidelines recommend that such nodules, when one centimeter or larger in size, should undergo further investigation with thyroid ultrasound (US) and fine-needle aspiration (FNA) cytology. Objectives: The objective of our study was to determine the rate of malignancy amongst TI discovered incidentally on 18F-FDG-PET or PET/CT, examine their clinicopathologic characteristics, and assess the usefulness of maximum standardized uptake values (SUV max) in differentiating benign and malignant lesions. Methods: We performed an electronic medical record search looking at all 18F-FDG-PET or PET/CT reports during the study period of 12/01/2015 to 05/31/2019 that included the keyword ‘thyroid’ in the impression. Exclusion criteria included a history of thyroid disease or malignancy, known lesion(s) detected on previous clinical or radiological examinations and diffuse radiotracer uptake. Of the 476 reports reviewed, 136 cases were included in the study. Results: Common indications included initial staging or restaging of lymphoma (diffuse large B-cell, mantle-cell, T-cell types) (27.9%), lung adenocarcinoma (18.4%), head and neck cancer (16.9%) and breast cancer (11%). Fifty-eight (42.6%) patients had metabolically inactive lesions; five (8.6%) underwent further investigation with thyroid US and 3 subsequently with FNA (5%). All 3 had benign cytology. Seventy-seven (56.6%) patients had metabolically active lesions and 25 (32.5%) underwent imaging with thyroid US. Twelve (15.6%) had FNA; eight (66.7%) had benign cytology, two (16.7%) revealed atypia of undetermined significance and two (16.7%) were malignant. Biopsy for the two patients with malignant cytology showed follicular cell neoplasm of oncocytic hurtle cell type, and invasive follicular carcinoma with focal insular and papillary features and extensive capsular and vascular invasion. The mean SUV max in malignant vs benign lesions was 9.05 and 6.41 respectively. Conclusion: The malignancy rate was 2.6% amongst all patients with 18F-FDG-avid TI and 8% amongst patients with metabolically active lesions who were investigated with thyroid US+/- FNA. This is significantly lower than malignancy rates previously reported in the literature. The evident inhomogeneity in the literature is likely multifactorial and may be explained in part by a dissimilarity among studies, and an informed decision by some to avoid invasive testing in the context of poor prognosis from underlying non-thyroidal cancer. Research is needed to determine the cohort of patients who could potentially benefit from further evaluation and treatment.

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          Author and article information

          Journal
          J Endocr Soc
          J Endocr Soc
          jes
          Journal of the Endocrine Society
          Oxford University Press (US )
          2472-1972
          03 May 2021
          03 May 2021
          03 May 2021
          : 5
          : Suppl 1 , ENDO 2021 Abstracts Annual Meeting of the Endocrine Society
          : A864-A865
          Affiliations
          [1 ] University of Maryland Medical Center Midtown Campus , Baltimore, MD, USA
          [2 ] American University of Antigua, Osbourn, Antigua and Barbuda
          [3 ] Division of Endocrinology, Diabetes, and Nutrition, University of Maryland School of Medicine , Baltimore, MD, USA
          Article
          bvab048.1765
          10.1210/jendso/bvab048.1765
          8089983
          d9e91858-7f14-4b6f-8b07-50cabd17537b
          © The Author(s) 2021. Published by Oxford University Press on behalf of the Endocrine Society.

          This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs licence ( http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reproduction and distribution of the work, in any medium, provided the original work is not altered or transformed in any way, and that the work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

          History
          Page count
          Pages: 2
          Categories
          Thyroid
          Thyroid Cancer
          AcademicSubjects/MED00250

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