What are the guidelines on diagnosis and management of familial MTC syndromes?

Updated: Jun 24, 2020
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Answer

The familial medullary thyroid carcinoma (MTC) syndromes consist of multiple endocrine neoplasia (MEN) types 2A and 2B and familial MTC. They are inherited in an autosomal dominant fashion. Children inheriting any of these syndromes have a 100% risk of developing MTC.

MEN 2A (Sipple syndrome) consists of MTC, pheochromocytoma (in 50% of patients), and hyperparathyroidism (10-20% of patients). MEN 2B consists of MTC, pheochromocytoma (in 50% of patients), marfanoid habitus, and ganglioneuromatosis. FMTC consists of MTC alone.

MTC in MEN 2B has the most aggressive biologic features. In this situation, MTC usually develops around 10 years of age, and it has a high propensity for rapid growth and metastasis. MTC in MEN 2A can appear in the first decade of life, and it almost always develops by the second decade. MTC in FMTC usually develops during adulthood.

Genetic testing is now the mainstay in the diagnosis of the familial MTC syndromes. Germline RET proto-oncogene mutations (on chromosome arm 10q) discovered in these syndromes include the following [2] :

  • MEN 2A – Majority of cases show substitutions of conserved cysteine residues in exons 10 and 11
  • MEN 2B – 95% of cases show threonine-for-methionine substitution in codon 918 of exon 16.
  • Familial MTC - Most commonly seen with mutations in exons 10, 13 & 14

Guidelines from the American Thyroid Association (ATA) recommend prophylactic thyroidectomy for individuals that have a documented RET mutation and are at risk for aggressive medullary thyroid carcinoma. [2]

The original ATA guidelines [2]  stratified risk level of RET carriers into four categories, A through D, based upon the increasing aggressiveness of the particular mutation. Due to some confusion and lack of uniformity with other staging guidelines, the revised ATA guidelines [4] transition category D to “highest risk” (HST), transition category C to “high risk” (H), and combine categories B and A into “moderate risk”. The risk stratification, screening schedules, and prophylactic thyroidectomy schedules are described in the table below.

Table. Revised ATA MTC Risk Levels and Pediatric Recommendations (Open Table in a new window)

Risk Level

RET codon Mutation

Possible Diagnoses

Prophylactic Thyroidectomy

Recommendations

Follow-up

Highest Risk (HST)

M918T+All MEN2B

MEN2B

Within the first year of life or the first months of life based upon specialist and parental discussions. The ability to identify and preserve or transplant parathyroid glands determines level VI dissection.

Physical exam, neck US, serum Ctn, and serum CEA every 6 mos first year, then annually; begin screening for pheochromocytoma at age 11 yr

High Risk (H)

C634, A883F

MEN2A

At or before age 5 yr, to be determined on the basis of serum Ctn

Physical exam, neck US, serum Ctn, and serum CEA every 6 mos first year, then annually. Begin screening for pheochromocytoma at age 11.

Moderate Risk (MOD)

All other mutations

MEN2A

When serum Ctn becomes elevated or in childhood to avoid lengthy evaluation period.

Evaluate every 6 months for 1 year. Annual follow-ups thereafter if serum Ctn is normal or undetectable. Begin screening for pheochromocytoma at age 16 yr

CEA=carcinoembryonic antigen;  Ctn=calcitonin; MEN=multiple endocrine neoplasia; US=ultrasound


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