Medullary thyroid carcinoma (MTC) secretes calcitonin as a tumour marker. In the RET proto-oncogene mutation landscape, which codon mutation is associated with the most aggressive MTC and mandates prophylactic thyroidectomy in the first 6 months of life?
- A Codon 634 (MEN2A highest risk)
- B Codon 918 (MEN2B — highest risk) ✓
- C Codon 620 (MEN2A moderate risk)
- D Codon 768 (FMTC lower risk)
Correct answer: B. Codon 918 (MEN2B — highest risk)
Explanation
RET codon 918 mutation (M918T) associated with MEN2B is classified as the highest risk (D — ATA Highest Risk Category), mandating thyroidectomy within 6 months of life or even in the neonatal period. MEN2B presents with mucosal neuromas, marfanoid habitus, and very aggressive MTC that can metastasise in infancy. Codon 634 mutations cause MEN2A and are high risk (prophylactic thyroidectomy by age 5). Codon 768 and 804 are moderate risk.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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