What tests are recommended for a patient with a history of thyroid nodules and type 2 diabetes being considered for semaglutide (glucagon-like peptide-1 receptor agonist) therapy to rule out Multiple Endocrine Neoplasia syndrome type 2 (MEN2)?

Testing for MEN2 Before Initiating Semaglutide

Before prescribing semaglutide to any patient, you must obtain a detailed personal and family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2 (MEN2), and if there is any suspicion, perform RET germline mutation testing—semaglutide is absolutely contraindicated in patients with MEN2. 1, 2

Mandatory Pre-Treatment Screening

Clinical History Assessment

• Ask every patient about personal history of MTC or family history of MTC in any first-degree relatives before prescribing any GLP-1 receptor agonist 3, 1
• Screen for family history of pheochromocytoma, as this raises suspicion for MEN2 even without known thyroid disease 3
• Inquire about oral or ocular neuromas (lips, tongue, sclera, eyelids) and diffuse ganglioneuromatosis or chronic constipation since childhood, which suggest MEN2B 3, 4
• Document any history of bilateral adrenal tumors or parathyroid disease in the patient or family members 5

Physical Examination Findings

• Examine for mucosal neuromas on lips, tongue, and oral mucosa, which are pathognomonic for MEN2B 4
• Look for characteristic MEN2B body habitus: tall and lanky build with elongated face and large lips 3
• Palpate the thyroid for nodules or masses in the neck 2

When to Order RET Genetic Testing

Absolute Indications for RET Testing

• Any patient with MTC (even apparently sporadic) should undergo RET germline mutation testing, as 25% of unselected MTC cases have a RET mutation 3
• Any first-degree relative of a patient with known MEN2 or MTC 6, 7
• Any patient with pheochromocytoma, particularly if bilateral, as 5% have RET mutations 3
• Any patient with the clinical phenotype of MEN2B (mucosal neuromas, marfanoid habitus, chronic constipation from birth) 4

Testing Methodology

• RET germline mutation testing detects mutations in 99% of MEN2 cases 5, 7
• The most common mutations occur in specific codons with distinct phenotypes 6, 8:
  • MEN2A: Mutations in exons 10,11 (codons 609,611,618,620,630) and exon 13 8, 9
  • MEN2B: Codon 918 mutation (M918T) in exon 16 in 95% of cases, or A883F in exon 15 in 2-3% 8, 4
• Multiplex PCR with heteroduplex analysis or direct DNA sequencing are the standard testing methods 9

Critical Decision Algorithm

If Family History is Positive or Suspicious:

1. Do NOT prescribe semaglutide until RET testing is completed 1, 2
2. Order RET germline mutation testing immediately 7
3. If RET mutation is confirmed, semaglutide is permanently contraindicated 1, 2
4. Consider alternative diabetes medications (SGLT2 inhibitors, other drug classes) 1

If Family History is Negative:

1. Proceed with semaglutide if no other contraindications exist 1
2. However, remember that 40-50% of MEN2B cases arise from de novo mutations 8
3. If patient has thyroid nodules, obtain baseline serum calcitonin before starting semaglutide 2

Biochemical Screening Considerations

Serum Calcitonin Testing

• Routine calcitonin monitoring is of uncertain value for early MTC detection in patients without known MEN2 2
• However, if calcitonin is measured and >50 ng/L, this strongly suggests MTC and warrants further evaluation including RET testing 2
• The FDA label notes that routine calcitonin monitoring may increase unnecessary procedures due to low specificity 2

When Calcitonin Testing May Be Useful:

• In patients with thyroid nodules being evaluated before semaglutide initiation 2
• If there is any clinical suspicion for MTC based on nodule characteristics 2

Additional Pre-Treatment Requirements for This Patient

Diabetic Retinopathy Assessment

Since this patient has type 2 diabetes and thyroid nodules, you must also obtain a comprehensive dilated eye examination before initiating semaglutide if one has not been performed within the last 12 months 10, 1

• Semaglutide carries increased risk of diabetic retinopathy complications, particularly in patients with pre-existing proliferative retinopathy 10, 2
• The mechanism relates to rapid A1C reduction rather than the drug itself 10

Common Pitfalls to Avoid

• Never assume sporadic MTC is truly sporadic—always test for RET mutations as 25% have germline mutations 3
• Do not rely solely on family history—up to 50% of MEN2B cases are de novo mutations 8
• Do not confuse MEN1 with MEN2—GLP-1 agonists are safe in MEN1 but absolutely contraindicated in MEN2 1
• Screen for family history before every GLP-1 prescription—this is a critical safety step that prevents prescribing a contraindicated medication 1
• Remember that early MEN2B may present only with gastrointestinal symptoms (chronic constipation, intestinal obstruction in infancy) before other features develop 4