Multiple Endocrine Neoplasia Type 2 (MEN2) Workup

Genetic testing is the mainstay in the diagnosis of multiple endocrine neoplasia type 2 (MEN2) syndromes. Perform genetic screening for RET mutations in all index patients. If a mutation is identified, also screen family members who are at risk. ^[8]

For individuals identified with a mutation or for persons who are at risk, biochemical screening consists of baseline calcitonin levels, serum calcium and parathyroid hormone (PTH) levels, along with urine collection for catecholamines and metanephrine concentrations. (However, a plasma metanephrine level can be used for screening.) Note that one fourth of patients with apparently sporadic pheochromocytoma may be carriers of mutations characteristic of syndromes associated with pheochromocytomas.

If a patient's calcitonin level is within reference ranges, a pentagastrin and/or Ca⁺⁺ stimulation test may be used as a guide to assess the necessity of a central compartment or modified neck dissection.

Patients who have been diagnosed with medullary thyroid carcinoma require serial calcitonin (with or without provocative testing) and carcinoembryonic antigen (CEA) testing after neck surgery to assess for persistent or recurrent disease.

Germline RET proto-oncogene mutations (on chromosome arm 10q) discovered in MEN2-related syndromes include the following:

• MEN2A – The majority of cases show substitutions of conserved cysteine residues in exons 10 and 11
• MEN2B – 95% of cases show threonine-for-methionine substitution in codon 918 of exon 16.
• Familial medullary thyroid carcinoma (FMTC) - Most commonly seen with mutations in exons 10, 13, and 14

Initial testing for MEN2A is either a single or multi-tiered analysis to detect RET mutations in the following:

• Exon 10 (codons 609, 611, 618, and 620)
• Exon 11 (codons 630 and 634)
• Exons 8, 13, 14, 15, and 16

Sequencing of the entire coding region should be reserved for situations in which no RET mutation is identified or the identified genotype is inconsistent with the MEN2 phenotype. 

Initial testing for MEN2B should be to detect the RET codon M918T mutation (exon 16), and if negative, then testing for the RET codon A883F mutation (exon 15) should be completed. If no mutations are identified in these two exons the entire RET coding region should be sequenced. ^[1]

 

Calcitonin is the principal biochemical marker in medullary thyroid carcinoma (MTC); measurement of calcitonin is used for detection, staging, postoperative management, and determining prognosis. The higher the calcitonin levels are above normal, the greater the likelihood of MTC; basal levels of >100 pg/mL have been found to have 100% positive predictive value for MTC. ^[1] Very rarely, patients with clinically apparent MTC may not have elevated calcitonin levels.

Traditionally, a pentagastrin-induced rise in calcitonin secretion has been used to diagnose MTC; however, pentagastrin is not available in the United States, and DNA testing for RET has replaced this diagnostic method in familial cases. In European countries, however, pentagastrim stimulation testing is used to further delineate extent of disease. 

Calcitonin and CEA determinations remain useful serologic tests to identify recurrent disease.

Urinary catecholamine and metanephrine levels screen for pheochromocytomas. If these are elevated, imaging studies of the adrenals are recommended.

Serum calcium and PTH levels screen for hyperparathyroidism. An inappropriately normal or elevated PTH level in relation to the elevated serum calcium is consistent with primary hyperparathyroidism. If the 24-hour urine calcium level is low, the presence of familial hypocalciuric hypercalcemic syndrome should be considered.

Perform computed tomography (CT) scanning or magnetic resonance imaging (MRI) of the adrenals. A metaiodobenzylguanidine (MIBG) or Dotatate scan is useful for localizing pheochromocytomas in case of non-visualization of pheochromocytomas by traditional radiologic studies..{ref17,26} ^{[17, 18]}

If calcitonin levels are elevated at either baseline or with provocative testing, evaluate the chest and abdomen for metastatic disease. Available modalities include CT scanning, MRI, octreotide scanning, and, in some instances, laparoscopy.

Radionuclide scanning may reveal the extent of metastasis. OctreoScan provides a whole-body examination and is used to examine the spread of medullary thyroid carcinoma. For this procedure the somatostatin analogue octreotide, which is used for the treatment of hormone-related symptoms, is labeled with the isotope indium-111 (¹¹¹In) and injected intravenously. The next day, the patient is examined with a gamma camera, which can detect the accumulation of radioactivity.

Fine-needle aspiration

Avoid the removal of cells from thyroid masses for cytology in patients with MEN2 who have had their diagnosis previously confirmed by either genetic analysis or elevated calcitonin levels. These patients have an established diagnosis, and a biopsy increases the possibility of tumor spread. A fine-needle aspiration biopsy is primarily used in an index patient who presents with a thyroid nodule when the clinician considers the presence of medullary thyroid carcinoma to be unlikely.

The tumor in medullary thyroid carcinoma is well demarcated, firm, and grayish white. Polygonal cells are uniform, with finely granular eosinophilic cytoplasm with central nuclei. Amyloid formed from calcitonin molecules is often found. Other findings include the following:

• C-cell hyperplasia - Frequently found; it is a precursor in the malignant transformation to medullary thyroid carcinoma.

• Pheochromocytomas - Benign tumors, often bilateral and multifocal, that arise from diffuse hyperplasia of the adrenal medulla

• Parathyroid hyperplasia - In this, overgrowth is the most common finding, although adenomatous changes occur in a small percentage of cases

TNM classification is used for postoperative staging. (T = the size of the primary lesion, N = the presence or absence of regional lymph node metastatic involvement, and M = the presence or absence of distant metastatic lesions.)

Primary lesions are designated as follows:

• T1 - Tumor 2 cm or less in greatest dimension, limited to the thyroid

• T2 - Tumor greater than 2 cm but no more than 4 cm; limited to the thyroid

• T3 - Tumor greater than 4 cm; limited to the thyroid

• T4a - Tumor of any size that extends extrathyroidally and invades subcutaneous soft tissues

• T4b - Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels

Regional lymph node metastatic involvement is designated as follows:

• N0 - No evidence of lymph node metastases

• N1 - Regional lymph node metastasis

• N1a - Metastasis to level VI (central compartment) cervical lymph node(s)

• N1b - Metastasis to unilateral or bilateral cervical nodes or to superior mediastinal lymph node(s)

Occurrence of distant metastatic lesions is designated as follows:

• M0 – No evidence of distant metastases exists

• M1 – Distant metastatic lesions exist

Postoperative staging is as follows:

• Stage 1 - T1,N0,M0

• Stage II - T2,N0,M0

• Stage III – (T3,N0,M0), (T1,N1a,M0), (T2,N1a,M0), (T3,N1a,M0)

• Stage IVA - (T4a,N0,M0), (T4a,N1a,M0), (T1,N1b,M0), (T2,N1b,M0), (T3,N1b,M0), (T4a,N1b,M0)

• Stage IVB - T4b, any N, M0

• Stage IVC - Any T, any N, and M1

Diagnostic studies for medullary thyroid cancer, primary hyperparathyroidism, pheochromocytoma, etc. as mentioned above