For a patient with a thyroid nodule that had fine‑needle aspiration showing a follicular neoplasm, oncocytic (Hürthle‑cell) type, should I wait for the Afirma gene expression classifier results before proceeding with thyroidectomy?

Do Not Wait for Afirma Testing Before Proceeding to Thyroidectomy

For a follicular neoplasm with oncocytic (Hürthle cell) features, you should proceed directly to thyroidectomy without waiting for Afirma results, as molecular testing performs poorly in this specific cytologic subtype and will not meaningfully change your management.

Why Molecular Testing Is Not Recommended for Hürthle Cell Neoplasms

The NCCN guidelines explicitly state that "molecular diagnostics are not recommended for Hürthle cell neoplasm" and note that "molecular diagnostics may not perform well for Hürthle cell neoplasms" 1. This recommendation stems from compelling evidence:

Historical Performance Problems

The older Afirma Gene Expression Classifier (GEC) showed unacceptably high false-positive rates for Hürthle cell lesions. In a key 2015 study, 86% of patients with suspicious Afirma GEC findings had unnecessary surgery—meaning the vast majority of "suspicious" results were actually benign nodules 1, 2. This represents a dramatic failure of the test's positive predictive value in this specific population.

Limited Improvement with Newer Tests

While newer molecular platforms (Afirma Genomic Sequencing Classifier and ThyroSeq v3) show some improvement, the NCCN panel concluded in 2018 that "the data were encouraging, they were not yet mature enough to make a recommendation for molecular testing in Hürthle cell lesions" 1. The panel members' clinical experiences consistently showed that false-positive rates for malignancy remained "unacceptably high" 1.

Even with the improved Afirma GSC, the specificity for Hürthle cell lesions was only 58.8%, meaning 41% of benign lesions still test as suspicious 1. ThyroSeq v3 showed slightly better specificity at 69.3%, but this still means nearly one-third of benign Hürthle cell nodules would be incorrectly classified 1.

The Standard Management Approach

For follicular neoplasm with oncocytic features (Bethesda Category IV), the standard approach is:

• Surgical excision is already indicated based on cytology alone, with an estimated malignancy risk of 15-40% 1
• The diagnosis of Hürthle cell carcinoma requires histologic examination to assess for capsular or vascular invasion, which cannot be determined by FNA or molecular testing 1
• Clinical risk factors, sonographic patterns, and patient preference should guide whether to perform lobectomy versus total thyroidectomy 1

Key Clinical Pitfalls to Avoid

1. Do not delay surgery waiting for molecular results that will likely be misleading
2. Do not be falsely reassured by a "benign" Afirma result in Hürthle cell lesions—the negative predictive value is not as robust as in non-Hürthle cell nodules
3. Do not automatically escalate to total thyroidectomy based on a "suspicious" molecular result—this will lead to overtreatment given the high false-positive rate

Practical Algorithm

For your patient with follicular neoplasm, oncocytic type:

1. Counsel the patient that surgery is recommended based on cytology alone
2. Discuss surgical options: lobectomy (preferred initial approach for most patients) versus total thyroidectomy based on:
   • Tumor size
   • Ultrasound features (extrathyroidal extension, suspicious lymph nodes)
   • Patient preference regarding potential need for completion surgery
   • Contralateral thyroid pathology
3. Proceed to surgery without molecular testing
4. Final diagnosis and further management will be determined by surgical pathology showing presence/absence of capsular or vascular invasion

The French consensus guidelines similarly acknowledge that while molecular testing may help reclassify some indeterminate nodules, the performance in oncocytic lesions remains problematic 3, 4. The focus should remain on surgical pathology as the definitive diagnostic tool for Hürthle cell neoplasms.