Guideline Recommendations for Screening and Management of MEN2A

Genetic Testing Strategy

• Germline RET testing should be performed in all individuals at risk for MEN2A as the primary screening tool; subsequent surveillance intensity and timing of prophylactic thyroidectomy are determined by the specific RET mutation risk category. [1][2]
• RET analysis detects pathogenic variants in approximately 99 % of MEN2 cases, enabling early identification of carriers before clinical disease manifests; a de novo mutation rate of about 9 % justifies testing even without a known family history. 2
• Genetic assessment is recommended to begin between ages 5 and 10 years for known at‑risk family members, with some experts advocating initiation as early as age 4 years for certain high‑risk mutations. 3

Risk Stratification by RET Genotype

High‑Risk Alleles (e.g., codons 634, 883)

• Prophylactic total thyroidectomy should be performed by age 5 years, or earlier if serum calcitonin becomes elevated. 2
• Annual thyroid ultrasound and serum calcitonin screening should commence at age 3 years. 2
• Metastatic disease is uncommon when serum calcitonin remains below 40 pg/mL. 2

Moderate‑Risk Alleles (e.g., codons 611, 620, others)

• Median age to develop medullary thyroid carcinoma (MTC) differs by codon: approximately 19 years for codon 620 versus 56 years for codon 611. [1][2]
• Surgery is advised when serum calcitonin shows an upward trend or when fine‑needle aspiration cytology confirms MTC. [1][2]
• If surgery is delayed, mandatory annual surveillance with serum calcitonin and thyroid ultrasound is required. [1][2]
• Thyroid ultrasound is less sensitive than calcitonin for detecting MTC and should not be used to exclude malignancy or postpone surgery. [1][2]

Biochemical Surveillance for Medullary Thyroid Carcinoma

• Annual measurement of serum calcitonin is the primary biochemical marker for MTC surveillance. [1][2]
• In infancy, physiological calcitonin levels may reach ≈ 50 pg/mL and decline over the first three years, limiting the test’s utility in very young children. 2
• Annual thyroid ultrasound serves as an adjunct to calcitonin testing but cannot replace it. [1][2]

Pheochromocytoma Screening

• Screening should start at age 11 years for carriers of high‑risk RET alleles and at age 16 years for moderate‑risk carriers. 1
• Recommended biochemical tests are plasma free metanephrines and normetanephrines (or 24‑hour urinary fractionated metanephrines). 1
• Biochemical screening must be performed before any planned surgery or pregnancy, irrespective of patient age. 1
• Imaging is reserved for abnormal biochemical results; magnetic resonance imaging of the abdomen/pelvis is preferred in pediatric patients to avoid ionizing radiation. 1
• Pre‑operative alpha‑adrenergic blockade is essential for patients with biochemically confirmed pheochromocytoma prior to any surgical intervention. 1

Hyperparathyroidism Screening

• Serum calcium screening should begin at age 11 years for high‑risk allele carriers and at age 16 years for moderate‑risk carriers. 1
• When hypercalcemia is detected, concurrent measurement of intact parathyroid hormone and assessment of 25‑OH vitamin D levels are recommended. 1
• Hypercalcemia with normal or elevated intact PTH confirms hyperparathyroidism and warrants referral to an experienced endocrinologist and surgeon. 1

Prophylactic Thyroidectomy Timing and Surgical Considerations

• Total thyroidectomy performed by surgeons experienced in MEN2 is the primary preventive strategy and effectively prevents subsequent biochemical evidence of disease. 2
• For the highest‑risk allele (p.M918T, associated with MEN2B), thyroidectomy should be carried out within the first year of life. 2
• For high‑risk alleles (codons 634, 883), thyroidectomy is recommended by age 5 years or earlier if calcitonin levels rise. 2
• For moderate‑risk alleles, thyroidectomy is indicated when calcitonin demonstrates an upward trend or when cytology confirms MTC. [1][2]
• Pre‑operative staging with thyroid ultrasound or cross‑sectional imaging (contrast‑enhanced neck CT or MRI) is essential to identify regional lymphadenopathy and guide surgical planning. 2

Multiple Endocrine Neoplasia Type 2 (MEN2) Diagnosis and Management

Genetic Basis of MEN2

• Multiple endocrine neoplasia type 2 (MEN2) results from pathogenic germline variants in the RET proto-oncogene, which is a receptor tyrosine kinase located on chromosome 10q11.21 4, 5
• The RET protein has an extracellular binding domain, a transmembrane domain, and an intracellular segment with a split tyrosine kinase domain 5
• Variants that strongly activate the intracellular tyrosine kinase domain are associated with earlier age of onset and more aggressive disease progression 5

Clinical Manifestations of MEN2

• MEN2 is subdivided into MEN2A and MEN2B based on clinical and genetic characteristics 4
• MEN2A is characterized by medullary thyroid carcinoma (MTC) with a greater than 95% lifetime risk, pheochromocytoma with a 50% risk, and primary hyperparathyroidism with a 20-30% risk 4, 5
• MEN2B presents with MTC with a 100% risk, often in infancy and more aggressive, pheochromocytoma with a 50% risk, mucosal neuromas, intestinal ganglioneuromatosis, marfanoid habitus, and no hyperparathyroidism 4, 5

Genotype-Phenotype Correlations in MEN2

• Strong genotype-phenotype correlations exist in MEN2, with clinical features predictably associated with specific codon mutations 4, 5
• The p.M918T variant in exon 16 is considered the highest risk variant and is associated with the majority of MEN2B cases 5
• Codon 634 variants are associated with higher risks of pheochromocytoma and hyperparathyroidism than other RET variants 5

Clinical Management and Testing Recommendations for MEN2

• Early diagnosis and prophylactic thyroidectomy are critical for MEN2B patients, ideally within the first year of life 5
• For patients with the highest risk allele (p.M918T), thyroidectomy is advised within the first year of life 5
• Genetic testing is essential for at-risk family members to guide surveillance and preventive interventions 6
• The de novo mutation rate is approximately 9% in MEN2A and as high as 50% in MEN2B 5
• Early identification of mutation carriers allows for preventive interventions that can significantly reduce morbidity and mortality 4, 5

NCCN and Genetics in Medicine Key Recommendations for MEN2 Management

Biochemical Surveillance

• Serum carcinoembryonic antigen (CEA) should be measured alongside calcitonin as a complementary tumor marker in individuals with RET mutations – NCCN guideline (2020) recommends routine CEA monitoring to aid early detection of medullary thyroid carcinoma progression. 7

Pre‑operative Evaluation and Surgical Precautions

• Assessment of vocal cord mobility is required before thyroidectomy in RET mutation carriers – NCCN advises pre‑operative laryngoscopic examination to identify recurrent laryngeal nerve involvement and plan surgery accordingly. 7
• Any coexisting pheochromocytoma must be diagnosed and treated prior to thyroid surgery – NCCN emphasizes that untreated pheochromocytoma can precipitate hypertensive crisis during thyroidectomy; appropriate biochemical screening and alpha‑adrenergic blockade are mandatory. 7
• Thyroid surgery must never be performed without first excluding and managing pheochromocytoma – NCCN states that proceeding to thyroidectomy without ruling out pheochromocytoma is a potentially fatal error. 7

Genetic Testing Recommendations

• RET genetic testing is not indicated for isolated, apparently sporadic hyperparathyroidism when there is no other clinical suspicion of MEN2 – Recommendations from Genetics in Medicine (2015) advise against routine RET analysis in such cases to avoid unnecessary testing. 8
• Approximately one‑quarter of unselected patients with medullary thyroid carcinoma (MTC) harbor a germline RET mutation, supporting universal RET testing in all newly diagnosed MTC cases – Evidence presented in Genetics in Medicine (2015) underscores the high yield of genetic screening regardless of family history. 8