What are the characteristics of Hürthle cell (Hürthle cell carcinoma) thyroid carcinoma?

Characteristics of Hürthle Cell Thyroid Carcinoma

Hürthle cell thyroid carcinoma is more aggressive than follicular thyroid carcinoma, cannot be reliably diagnosed by fine-needle aspiration alone, and typically shows poor uptake of radioactive iodine. 1, 2

Classification and Pathology

• Hürthle cell carcinoma (HCC) represents approximately 3% of all thyroid carcinomas 1
• HCC is now classified as a distinct type of differentiated thyroid cancer by the World Health Organization, rather than being considered a variant of follicular thyroid carcinoma 1, 3
• "Pure" Hürthle cell carcinomas are defined as those with a Hürthle-cell component exceeding 75% of the tumor 1
• HCC presents with molecular abnormalities that distinguish it from conventional follicular carcinomas 4

Diagnostic Challenges

• HCC cannot be definitively diagnosed by fine-needle aspiration (FNA) alone, as cytology cannot reliably distinguish between benign and malignant Hürthle cell neoplasms 1
• Definitive diagnosis requires histological evidence of capsular and/or vascular invasion, which can only be determined after surgical excision 1, 3
• Molecular diagnostics are not recommended for Hürthle cell neoplasms due to high false-positive rates for malignancy 1

Aggressiveness and Prognosis

• HCC is more aggressive than follicular thyroid carcinoma, with higher rates of recurrence and mortality 5, 2
• The 10-year relative survival rate for Hürthle cell carcinoma is approximately 76%, which is lower than papillary (93%) and follicular (85%) carcinomas 1
• The risk of recurrence is classified as high (30-55%) when HCC is associated with extensive vascular invasion (>4 foci) 1, 3
• HCC is generally less likely to present with lymph node metastases compared to other high-risk thyroid carcinomas, but when metastases occur, they indicate a worse prognosis 4

Radiation Association

• Unlike some other thyroid cancers, there is no established association between Hürthle cell carcinoma and previous neck radiation exposure 1
• Only rare cases have been reported with a history of low-dose external radiation to the head and neck in childhood 6

Radioactive Iodine Uptake

• Fewer than 10% of Hürthle cell carcinomas take up radioactive iodine effectively, making this treatment modality less useful than in other differentiated thyroid cancers 5
• The effectiveness of radioactive iodine therapy for HCC remains debated in the literature 2
• Some studies report successful radioiodine ablation therapy for residual thyroid tissue, with most patients requiring only a single dose 6

Treatment Approach

• Total thyroidectomy is the standard treatment for Hürthle cell carcinoma, not lobectomy, due to its more aggressive behavior 1
• If lymph nodes are positive, central neck dissection (level VI) and lateral neck dissection (levels II-IV) are recommended 1
• All patients should receive TSH suppression therapy with levothyroxine 1
• Recurrent disease is treated surgically with good palliation and appreciable prolongation of life 5

Clinical Pearls and Pitfalls

• Pitfall: Treating HCC with lobectomy alone can lead to inadequate management of this potentially more aggressive cancer 1
• Pitfall: Relying solely on fine-needle aspiration for diagnosis can lead to misdiagnosis, as definitive diagnosis requires histological examination of the surgical specimen 1, 3
• Pearl: HCC with extensive vascular and/or capsular invasion should be managed like other high-risk carcinomas 4