What is the recommended treatment for medullary thyroid carcinoma, including surgical management, systemic therapy, and management of metastatic disease?

Treatment of Medullary Thyroid Cancer

For patients with progressive, metastatic medullary thyroid cancer (MTC) who harbor RET mutations, selpercatinib is the preferred first-line systemic therapy (category 1), demonstrating superior progression-free survival, response rates (73% in first-line), and tolerability compared to cabozantinib or vandetanib. 1, 2

Surgical Management

Surgery remains the only curative option and should be performed early when feasible 3. The extent of surgery depends on:

• Tumor burden and locoregional spread
• Calcitonin trajectory and structural doubling times - these are critical biomarkers that inform prognosis, surgical extent, likelihood of residual disease, and need for additional therapy 3
• Germline RET testing results - universal testing is mandatory to distinguish hereditary from sporadic disease 4

For hereditary MTC, prophylactic thyroidectomy may be indicated based on RET mutation risk stratification 5.

Systemic Therapy for Advanced/Metastatic Disease

When to Initiate Systemic Therapy

Do NOT treat based on rising calcitonin or CEA alone - systemic therapy is reserved for radiographically evident structural disease that is either symptomatic or progressive 1. Asymptomatic patients with low tumor burden and stable disease can be monitored with imaging every 6-12 months, adjusted based on calcitonin and CEA doubling times 6.

First-Line Systemic Therapy Algorithm

Step 1: Determine RET mutation status (somatic testing if germline wild-type or unknown) 1

Step 2: If RET mutation-positive:

• Preferred: Selpercatinib (category 1) 1, 2

  • Response rate: 73% in treatment-naive patients
  • Maintained at 1 year in 93% of cases
  • Superior tolerability: only 4.8% treatment discontinuation vs. 27% with cabozantinib/vandetanib
  • Dose reductions needed in 39% vs. 77% with multikinase inhibitors
  • The LIBRETTO-531 phase III trial demonstrated 72% reduction in disease progression risk compared to cabozantinib/vandetanib 2
  • FDA approved for pediatric patients ≥2 years old 1

• Alternative: Pralsetinib (category 2B) - another RET-specific inhibitor with 71% response rate in first-line and 60% in second-line 7

Step 3: If RET mutation-negative or after progression on RET inhibitors:

• Cabozantinib (category 1) - FDA approved in 2012, effective in both sporadic and familial MTC 1

  • Contraindication: History of severe hemorrhage
  • Rare but serious adverse events: severe bleeding, GI perforations, fistula formation

• Vandetanib (category 1) - requires REMS program certification for prescribing and dispensing 1

Why RET-Specific Inhibitors Are Preferred

The evidence strongly favors selpercatinib over traditional multikinase inhibitors when RET mutations are present. The phase III EXAM and ZETA trials with cabozantinib and vandetanib showed progression-free survival benefit but no evidence of prolonged overall survival 7. In contrast, selpercatinib provides:

• Higher response rates (73% vs. 40%)
• Better tolerability profile
• Fewer dose reductions and discontinuations
• Maintained response at 1 year 2

Second-Line and Beyond

For patients previously treated with cabozantinib or vandetanib, selpercatinib maintains a 69% response rate 2. Other options for symptomatic disease or progression include:

• Other small-molecule kinase inhibitors (sunitinib, sorafenib, lenvatinib, pazopanib) 1
• Dacarbazine-based chemotherapy regimens 1

Locoregional Treatments

For oligometastatic or localized progressive disease, consider:

• Surgical resection of isolated metastases
• Radiotherapy
• Interventional radiology procedures 2

These modalities should be integrated into a multimodal strategy based on tumor extent, progression pattern, and molecular characteristics 2.

Critical Pitfalls to Avoid

1. Do not initiate toxic systemic therapy for indolent, asymptomatic disease - many patients have slowly progressive disease where treatment risks outweigh benefits 1

2. Do not treat rising biomarkers alone - calcitonin and CEA elevation without structural disease on imaging is not an indication for systemic therapy 1

3. Do not skip RET testing - this is essential for selecting optimal first-line therapy, as RET-specific inhibitors offer dramatically better outcomes than multikinase inhibitors in RET-mutated disease 1, 2

4. Monitor for serious adverse events with multikinase inhibitors: bleeding, hypertension, liver toxicity, GI perforation - most are manageable but require proactive monitoring 1

5. Anticipate resistance mechanisms - while RET-specific inhibitors show excellent initial responses, resistance development remains a challenge requiring ongoing research 7, 8