We report a case of familial medullary thyroid carcinoma in an 87-year-old woman, despite the patient having a high-risk codon 620 mutation.

Medline and PubMed were searched for cases and literature reviews relating to the following keywords: ‘codon 620’, ‘medullary thyroid carcinoma’, ‘multiple endocrine neoplasia’ and ‘RET proto-oncogene’.

We report the case of an 87-year-old woman who presented with a goitre, later identified as medullary thyroid carcinoma. Genetic analysis revealed a RET proto-oncogene codon 620 mutation. Genetic testing has revolutionised the management of medullary thyroid carcinoma. The genetic basis of hereditary medullary thyroid carcinoma lies with the RET proto-oncogene. Several disease-causing mutations of this gene have been identified and their clinical prognosis described. The penetrance of these mutations is high; as such, carriers progress to develop medullary thyroid carcinoma at a young age. Mutations at the codon 620 position are classified as high-risk for early development of medullary thyroid carcinoma; thus, the current recommendation is for prophylactic thyroidectomy at five years of age.

In this case, the progress of hereditary medullary thyroid carcinoma was unique, considering the late presentation of medullary thyroid carcinoma despite the presence of the high-risk RET proto-oncogene codon 620 mutation. The authors wish to highlight the importance of this case, as it may present a counter-argument to the current recommendations for early, prophylactic thyroidectomy in codon 620 mutation carriers in order to prevent early development of medullary thyroid carcinoma.