What is the Bethesda system for assessing malignancy risk in thyroid cancer?

Updated: May 09, 2018
  • Author: Pramod K Sharma, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

Cytologic analysis of FNAB specimens is used to estimate malignancy risk. The most appropriate cytologic classification of malignancy risk is the Bethesda system for thyroid cytopathology, which includes the following categories [36, 37] :

  • Nondiagnostic or unsatisfactory (risk 5-10%)
  • Benign (risk 0-3%)
  • Atypia of undetermined significance or follicular lesion of undetermined significance (risk ∼10-30%)
  • Follicular neoplasm or suspicious for follicular neoplasm (risk 25-40%)
  • Suspicious for malignancy (risk 50-75%)
  • Malignant (risk 97-99%)

A 2017 revision to the Bethesda system includes a second set of malignancy risks for these six categories, one that calculates what these risks would be if noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP) were not classified as a malignancy. The adjusted risks for the six categories would be as follows [37, 38] :

  • Nondiagnostic or unsatisfactory (risk 5-10%)
  • Benign (risk 0-3%)
  • Atypia of undetermined significance or follicular lesion of undetermined significance (risk 6-18%)
  • Follicular neoplasm or suspicious for follicular neoplasm (risk 10-40%)
  • Suspicious for malignancy (risk 45-60%)
  • Malignant (risk 94-96%)

For cytology “diagnostic of” or “suspicious for” papillary thyroid cancer, surgery is recommended. [1]

If FNAB cytology is indeterminate, the use of molecular markers such as BRAF, RAS, RET/PTC, Pax8-PPARɣ, or galectin-3 may be considered to guide management. [1]

An iodine-123 (123I) thyroid scan may be considered if the cytology report documents a follicular neoplasm, especially if serum thyroid-stimulating hormone (TSH) is in the low-normal range. [1] No radionuclide scan is needed for a reading of “suspicious for papillary carcinoma” or “Hürthle cell neoplasm”, as either lobectomy or total thyroidectomy is recommended depending on the nodule size and risk factors. [1]


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