How is the malignancy risk of differentiated thyroid cancers determined?

Updated: Jun 24, 2020
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Answer

Cytological analysis of FNAB specimens is used to estimate malignancy risk. The most appropriate cytological classification of malignancy risk is the Bethesda system for thyroid cytopathology, which comprises the following categories [10] :

  • Malignant (risk 97-99%)
  • Suspicious for malignancy (risk 60-75%)
  • Follicular neoplasm or suspicious for follicular neoplasm (risk 15-30%)
  • Atypia of undetermined significance or follicular lesion of undetermined significance (risk 5-15% based on repeated atypicals)
  • Non-diagnostic or unsatisfactory (risk 1-4%)
  • Benign (risk 0-3%)

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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