What is the next systemic therapy for metastatic papillary thyroid cancer that progressed on lenvatinib and has become radioactive iodine (RAI)-non‑avid?

Cabozantinib is the Next-Line Treatment

For metastatic papillary thyroid cancer that has progressed on lenvatinib and remains RAI-refractory, cabozantinib is the recommended next-line systemic therapy 1, 2.

Evidence Base

The COSMIC-311 phase III randomized trial specifically evaluated cabozantinib versus placebo in patients with RAI-refractory differentiated thyroid cancer (including papillary histology) who progressed during or after 1-2 prior VEGFR tyrosine kinase inhibitors (including lenvatinib and sorafenib). The trial demonstrated:

• Median PFS: 11.0 months with cabozantinib vs 1.9 months with placebo (HR 0.22; 95% CI 0.15-0.32; P <0.0001) 1
• PFS benefit of 6.7 months 2
• Overall response rate: 11.0% vs 0% 1
• Category 1 recommendation for papillary carcinoma specifically 1

Subgroup analyses confirmed cabozantinib's efficacy regardless of whether patients previously received lenvatinib or sorafenib, making it the evidence-based choice for your specific scenario 1.

Alternative Considerations Based on Molecular Testing

Before initiating cabozantinib, obtain molecular testing if not already done 3. If actionable alterations are identified:

• RET fusion-positive disease: Selpercatinib (ORR 79%, median PFS 20.1 months) or pralsetinib (ORR 89%) are superior options 2
• NTRK fusion-positive disease: Larotrectinib (ORR 79%) or entrectinib (ORR 57%) 2
• ALK fusion-positive disease: Selective ALK inhibitors 3

These selective inhibitors demonstrate higher response rates and longer progression-free survival than cabozantinib in fusion-positive disease, making molecular testing critical before proceeding with cabozantinib 2.

Other Options When Cabozantinib is Not Feasible

If the patient cannot tolerate a second TKI but had manageable toxicity on lenvatinib, adding pembrolizumab to continued lenvatinib is a reasonable alternative. A multicenter cohort study showed 16% ORR and 10.0-month PFS with this combination in patients who progressed on lenvatinib 1.

For patients with more dedifferentiated disease who cannot tolerate TKIs, pemetrexed plus carboplatin may be considered, though this is based on case series data 1.

Important Caveats

• Serious treatment-related adverse events occurred in 16% of patients on cabozantinib (vs 2% placebo), though no treatment-related deaths occurred 1
• Avoid cabozantinib in patients with untreated CNS metastases due to bleeding risk 1
• The decision assumes progressive and/or symptomatic disease; kinase inhibitor therapy may not be appropriate for stable or slowly progressive indolent disease 1

Clinical Algorithm

1. Confirm progression on lenvatinib with imaging
2. Obtain molecular testing if not previously done (RET, NTRK, ALK fusions; BRAF mutations)
3. If fusion-positive: Use selective inhibitor (selpercatinib, pralsetinib, larotrectinib, entrectinib)
4. If no actionable alterations: Initiate cabozantinib as standard second-line therapy
5. If cabozantinib intolerant but lenvatinib was tolerable: Consider adding pembrolizumab to lenvatinib