What are the latest systemic treatment options for adult patients with metastatic thyroid cancer that is not amenable to surgery or radioactive iodine, based on tumor histology and molecular alterations?

Latest Treatment for Metastatic Thyroid Cancer

The latest systemic treatments for metastatic thyroid cancer are now molecularly-driven and histology-specific, with selective RET inhibitors (selpercatinib, pralsetinib) and NTRK inhibitors (larotrectinib, entrectinib) representing the most recent therapeutic advances, alongside cabozantinib as second-line therapy for radioactive iodine-refractory differentiated thyroid cancer. 1

Treatment Algorithm by Histology

Differentiated Thyroid Cancer (DTC) - RAI-Refractory

First-Line Therapy:

• Lenvatinib or sorafenib remain standard first-line multikinase inhibitors (MKIs) for progressive, RAI-refractory DTC 2
• Lenvatinib achieves higher response rates (ORR 57.3%) compared to sorafenib (ORR 40.3%) 1

Molecular Testing is Critical:

• Next-generation sequencing (NGS) should be performed before initiating systemic therapy to identify actionable mutations 1
• This testing guides selection of targeted therapies over non-selective MKIs

Molecularly-Targeted First-Line Options (if mutations present):

For RET fusion-positive DTC:

• Selpercatinib (160 mg twice daily for patients ≥50 kg; 120 mg twice daily for <50 kg):

  • In Europe: approved only after prior MKI therapy (sorafenib/lenvatinib) with 79% ORR 1
  • In United States: approved regardless of prior MKI therapy with 100% ORR in treatment-naive patients 1
  • Median duration of response: 18.4 months 1

• Pralsetinib (FDA-approved in US only):

  • For patients ≥12 years with RAI-refractory RET fusion-positive DTC
  • ORR: 89% in previously treated patients, 71% in treatment-naive 1
  • Duration of response: >9-12 months 1

For NTRK fusion-positive DTC:

• Larotrectinib: ORR 79% across solid tumors, 42.9% specifically in thyroid cancer 1
• Entrectinib: ORR 57% with manageable toxicity (grade 3-4 events: weight gain 10%, anemia 12%) 1
• Both approved for patients without satisfactory treatment options 1

Second-Line Therapy:

• Cabozantinib 60 mg once daily (tablet formulation) for patients progressing after lenvatinib or sorafenib 1
• Median PFS not reached vs 1.9 months with placebo (HR 0.22) 1
• ORR: 15% with significant PFS benefit maintained across all prior MKI subgroups 1
• Dose reductions required in 56% due to adverse events (palmar-plantar erythrodysesthesia, hypertension, fatigue) 1

Medullary Thyroid Cancer (MTC)

First-Line Therapy:

• Cabozantinib (140 mg once daily capsule formulation - NOT interchangeable with 60 mg tablet) or vandetanib 2
• Cabozantinib provides PFS and OS advantages, particularly in RET M918T or RAS-mutant MTCs 2

Molecularly-Targeted Options for RET-mutant MTC:

• Selpercatinib:

  • ORR 73% in treatment-naive patients 1
  • ORR 69% in patients previously treated with cabozantinib/vandetanib 1
  • Median duration of response: 22.0 months 1

• Pralsetinib:

  • ORR 71% in treatment-naive patients 1
  • Duration of response: >12 months 1

Key Decision Point: RET-selective inhibitors (selpercatinib, pralsetinib) show superior response rates compared to non-selective MKIs and should be prioritized when RET mutations are present 1, 3

Anaplastic Thyroid Cancer (ATC)

BRAF V600E-Positive ATC:

• Dabrafenib 150 mg twice daily + trametinib 2 mg once daily is the standard treatment 1
• This combination is FDA-approved and represents the only effective systemic therapy for BRAF-mutated ATC

For Other Molecular Alterations:

• RET or NTRK fusions: use selective inhibitors (selpercatinib, pralsetinib, larotrectinib, entrectinib) 1
• Non-druggable mutations: immunotherapy is an alternative 1
• Spartalizumab showed 19% response rate (29% in PD-L1 positive tumors) in phase II study 1

Critical Treatment Principles

Sequencing Strategy: The optimal sequence of MKIs versus selective kinase inhibitors cannot be definitively determined from current evidence 1. However, the decision algorithm should prioritize:

1. Molecular testing first - NGS is preferred approach 1
2. If actionable mutation present (RET, NTRK, BRAF V600E): use selective inhibitor
3. If no actionable mutation: lenvatinib or sorafenib for DTC; cabozantinib or vandetanib for MTC
4. Second-line after MKI progression: cabozantinib for DTC

Common Pitfalls:

• Using cabozantinib capsule (140 mg for MTC) and tablet (60 mg for DTC) interchangeably - they are NOT bioequivalent 1
• Starting systemic therapy in indolent disease without clear progression - watchful waiting may be appropriate
• Failing to perform molecular testing before treatment initiation, missing opportunities for targeted therapy
• Not considering dose reductions proactively - 56% of cabozantinib patients required dose reduction for toxicity management 1

Toxicity Management:

• Grade 3-4 treatment-related adverse events occur in 57-71% with cabozantinib 1
• Most common: palmar-plantar erythrodysesthesia (10%), hypertension (9%), fatigue (8%) 1
• Selpercatinib: 65% of patients experienced dose-limiting toxicities requiring management 1
• Early dose reduction is preferable to treatment discontinuation

Emerging Considerations:

• Redifferentiation therapy with MAPK inhibitors before radioactive iodine shows promise (33-95% iodine uptake restoration) but lacks randomized data 4
• Immunotherapy combinations with checkpoint inhibitors are under investigation 5

The treatment landscape has fundamentally shifted from empiric MKI therapy to precision medicine based on molecular profiling, with selective inhibitors demonstrating superior response rates and durability compared to non-selective agents when targetable alterations are present 1.