Adjuvant Treatment After Total Thyroidectomy for Medullary Thyroid Carcinoma
Adjuvant radiation therapy is not routinely necessary after total thyroidectomy for medullary thyroid carcinoma, but should be considered for patients with gross extrathyroidal extension (T4a or T4b) with positive margins after resection of all gross disease, or for those with moderate-to-high volume disease in the central or lateral neck lymph nodes with extranodal soft tissue extension. 1
Evidence Base for Adjuvant Radiation
External-beam radiation therapy has not been adequately studied as adjuvant therapy in medullary carcinoma, and most centers do not have extensive experience with adjuvant RT for this disease. 1 The evidence supporting its use is limited:
Slight improvements in local disease-free survival have been reported for selected patients with extrathyroidal invasion or extensive locoregional node involvement, but these benefits are modest. 1
A SEER database analysis of patients who underwent total thyroidectomy and lymph node excision between 1988-2004 found that after 12 years, EBRT did not significantly improve overall survival (log rank, P < 0.14). 2 While univariate analysis suggested a benefit in node-positive patients, multivariate analysis controlling for known prognostic factors could not duplicate this benefit. 2
Specific Indications for Adjuvant Radiation
Consider adjuvant external-beam RT for:
Gross extrathyroidal extension (T4a or T4b) with positive margins after resection of all gross disease 1
Moderate-to-high volume disease in the central or lateral neck lymph nodes with extranodal soft tissue extension 1
Important caveat: This practice is rarely recommended in children. 1
Radiation Technique When Used
When external-beam RT is administered, the typical regimen is:
40 Gy in 20 fractions to the cervical, supraclavicular, and upper mediastinal lymph nodes over 4 weeks 1
Subsequent booster doses of 10 Gy in 5 fractions to the thyroid bed 1
Essential Postoperative Management (Not Adjuvant Therapy)
All patients require postoperative levothyroxine to normalize TSH (not suppress it, as C cells lack TSH receptors). 1, 3
Measure basal serum calcitonin and CEA 2-3 months postoperatively to assess for residual disease. 1 This is critical because:
Approximately 80% of patients with palpable MTC and 50% with nonpalpable but macroscopic MTC have serum calcitonin values indicative of residual disease after supposedly curative resection. 1
Postoperative calcitonin levels < 150 pg/mL suggest disease confined to cervical lymph nodes if present. 4
Calcitonin levels > 1000 pg/mL suggest distant metastases, most likely in the liver. 1
Why Adjuvant Systemic Therapy Is Not Standard
MTC cells do not concentrate radioactive iodine, so radioiodine treatment is not effective. 1, 3 Conventional cytotoxic chemotherapy has shown very limited efficacy, achieving only partial responses in 10-20% of cases with short duration. 3 Systemic therapy with tyrosine kinase inhibitors is reserved for progressive metastatic disease, not as adjuvant treatment. 4, 3
Common Pitfall to Avoid
Do not routinely recommend adjuvant radiation for all patients after total thyroidectomy. The evidence does not support this approach, and surgery remains the definitive treatment for MTC. 1, 2 Reserve radiation for the specific high-risk features outlined above, recognizing that even in these cases, the survival benefit is uncertain. 2