What is the next systemic therapy for metastatic Hurthle‑cell carcinoma of the thyroid after progression on lenvatinib?

Cabozantinib is the recommended next-line systemic therapy for metastatic Hurthle cell carcinoma after lenvatinib progression

For metastatic Hurthle cell (oncocytic) thyroid carcinoma progressing on lenvatinib, cabozantinib is the evidence-based second-line treatment of choice. This recommendation is based on the phase III COSMIC-311 trial, which specifically included patients with oncocytic (Hurthle cell) differentiated thyroid cancer who progressed after prior VEGFR tyrosine kinase inhibitor therapy 1, 2.

Evidence Supporting Cabozantinib

The COSMIC-311 trial demonstrated robust efficacy in the post-lenvatinib setting:

• Median PFS: 11.0 months with cabozantinib versus 1.9 months with placebo (HR 0.22; 95% CI 0.15-0.32) 1
• Subgroup analysis confirmed benefit across all histologic subtypes, including oncocytic (Hurthle cell) carcinoma 1
• Benefit was maintained regardless of prior TKI: whether patients received lenvatinib, sorafenib, or both 1, 2
• Overall response rate: 11% versus 0% for placebo 1

This represents a Category 1 recommendation for papillary carcinoma and Category 2A for follicular and oncocytic carcinoma in NCCN guidelines 1.

Practical Considerations for Cabozantinib

Dosing and Toxicity Management

• Grade 3-4 treatment-related adverse events occurred in 57% of patients 2
• Most common serious toxicities: palmar-plantar erythrodysesthesia (10%), hypertension (9%), and fatigue (8%) 2
• 56% required initial dose reduction, 22% needed secondary reduction 2
• Only 5% discontinued due to adverse events 2
• No treatment-related deaths occurred 2

Key Safety Caveat

Avoid cabozantinib in patients with untreated CNS metastases due to associated bleeding risk 1.

Alternative Options When Cabozantinib is Not Feasible

If RET Fusion is Present

Test for RET fusions before selecting therapy. If an RET fusion is identified:

• Selpercatinib achieved 79% ORR in RET fusion-positive differentiated thyroid cancer (including one Hurthle cell case in the LIBRETTO-001 trial) with median PFS of 20.1 months 2
• Pralsetinib showed 89% ORR in similar patients 2

Both selective RET inhibitors are approved for use after lenvatinib/sorafenib failure in RET fusion-positive disease 2.

If Patient Cannot Tolerate Second TKI

If toxicity profile on lenvatinib was manageable but disease progressed, consider adding pembrolizumab to continued lenvatinib 1. A multicenter study showed:

• 16% ORR when pembrolizumab added to lenvatinib at progression
• Median PFS: 10.0 months (95% CI 7.0-17.9) 1

This approach is reasonable only when the patient tolerated lenvatinib well and cannot receive cabozantinib.

Other Molecular Targets

• NTRK fusions: Larotrectinib (79% ORR) or entrectinib (57% ORR) if present 2
• BRAF V600E mutations: Dabrafenib plus trametinib (though less common in Hurthle cell carcinoma)

Treatment Algorithm

1. Confirm progression on lenvatinib by RECIST 1.1 criteria
2. Obtain molecular testing if not previously done (RET, NTRK, ALK fusions; BRAF mutations)
3. If actionable fusion/mutation present: Use corresponding selective inhibitor (selpercatinib/pralsetinib for RET, larotrectinib/entrectinib for NTRK)
4. If no actionable target: Initiate cabozantinib as standard second-line therapy
5. If cabozantinib contraindicated/not tolerated and lenvatinib was well-tolerated: Consider pembrolizumab + lenvatinib continuation

Important Clinical Pitfalls

Do not continue lenvatinib monotherapy after clear progression unless adding pembrolizumab or awaiting molecular testing results. The evidence for lenvatinib rechallenge exists 3, 4 but is limited to small retrospective series and should not be first choice when cabozantinib has Level 1 evidence.

Do not delay molecular testing until after second-line failure. Hurthle cell carcinomas can harbor RET fusions (though less commonly than papillary thyroid cancer), and selective inhibitors offer superior response rates compared to multikinase inhibitors 2.

Recognize that Hurthle cell carcinoma is typically less radioiodine-avid than other differentiated thyroid cancers 5, making systemic therapy sequencing particularly important for long-term disease control.