Multiple Endocrine Neoplasia Syndromes¶
Chapter 400 | Part 12: Endocrinology
KEY CLINICAL POINTS¶
- Multiple Endocrine Neoplasia (MEN) syndromes are inherited disorders characterized by tumors in two or more endocrine glands, with MEN1 (11q13), MEN2A (10q11.2), MEN2B (10q11.2), and MEN4 (12p13) being the most common types.
- MEN1 is associated with parathyroid, pancreatic, and pituitary tumors, while MEN2A and MEN2B are linked to medullary thyroid carcinoma (MTC), pheochromocytoma, and parathyroid tumors.
- Genetic testing is critical for diagnosis, with mutations in MEN1, RET, SDH genes, and CDKN1B playing key roles in pathogenesis.
- Management includes surgical resection, somatostatin analogs, and targeted therapies like selpercatinib for advanced MTC.
- Screening protocols (e.g., annual biochemical tests, imaging) are essential for early detection of tumors in at-risk individuals.
1. DEFINITION & OVERVIEW¶
Multiple Endocrine Neoplasia (MEN) syndromes are autosomal dominant disorders characterized by tumors in two or more endocrine glands. Five major types (MEN1–MEN5) and six other syndromes (MEONs) are recognized. MEN1 (11q13) involves parathyroid, pancreatic, and pituitary tumors; MEN2A (10q11.2) and MEN2B (10q11.2) are linked to MTC, pheochromocytoma, and parathyroid tumors. Other syndromes include von Hippel-Lindau (VHL), neurofibromatosis (NF1), and Cowden’s syndrome (CWS).
Table 400-1: Multiple Endocrine Neoplasia (MEN) Syndromes¶
| TYPE | TUMORS (ESTIMATED PENETRANCE) | GENE AND MOST FREQUENTLY MUTATED CODONS |
|---|---|---|
| MEN 1 (11q13) | Parathyroid adenoma (90%) | MEN1 (83/84, 4-bp del) |
| MEN 2A (10q11.2) | MTC (90%) | RET (Ex8, Ex10, Ex11) |
| MEN 2B (10q11.2) | MTC (90%) | RET (Ex16, 918MetfiThr) |
| MEN 4 (12p13) | Parathyroid adenoma | CDKN1B (no common mutations) |
| MEN 5 (14q23.3) | Pheochromocytoma | MAX (no common mutations) |
1.1 Genetic Basis¶
MEN1 is caused by mutations in the MEN1 gene (11q13), while MEN2A and MEN2B result from RET gene mutations. VHL disease involves the VHL gene (3p25), and CWS is associated with PTEN, SDHB, SDHD, and other genes. These syndromes follow the Knudson two-hit hypothesis for tumor suppressor genes.
1.2 Clinical Features¶
MEN1 presents with parathyroid adenomas, pancreatic NETs, and pituitary tumors. MEN2A/MEN2B includes MTC, pheochromocytoma, and parathyroid tumors. VHL involves hemangioblastomas, RCC, and pheochromocytoma. NF1 is marked by neurofibromas, café au lait spots, and optic gliomas.
2. EPIDEMIOLOGY¶
MEN1 has a prevalence of ~0.25% (1 in 4000), with 1–18% among patients with primary hyperparathyroidism. MEN2A occurs in 1 in 35,000, while MEN2B is rarer. VHL disease has an incidence of 1 in 35,000. NF1 affects 1 in 3000, and CWS has an incidence of 1 in 100,000. Risk factors include family history and germline mutations.
Table 400-2: Multiple Endocrine and Other Organ Neoplasia (MEON) Syndromes¶
| DISEASE | GENE PRODUCT | CHROMOSOMAL LOCATION |
|---|---|---|
| Hyperparathyroidism-jaw tumor (HPT-JT) | Parafibromin | 1q31.2 |
| von Hippel–Lindau (VHL) | pVHL (elongin) | 3p25 |
| Cowden’s syndrome (CWS1) | PTEN | 10q23.31 |
| Cowden’s syndrome (CWS2) | SDHB | 1p36.13 |
| Cowden’s syndrome (CWS3) | SDHD | 11q23.1 |
2.1 Demographics¶
MEN1 is more common in women (1:1 ratio). VHL and NF1 show equal gender distribution. CWS is more prevalent in women, with 75% of breast abnormalities. MEN2A and MEN2B are more common in males.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
MEN1 is caused by inactivating mutations in the MEN1 gene (11q13), leading to loss of tumor suppressor function. RET mutations (10q11.2) drive MTC and pheochromocytoma in MEN2A/B. VHL mutations (3p25) disrupt pVHL function, leading to VEGF overexpression and angiogenesis. CWS involves PTEN, SDHB, SDHD, and other genes, with genomic instability and mosaicism playing roles.
3.1 Molecular Mechanisms¶
MEN1 follows the Knudson two-hit hypothesis. RET mutations in MEN2A/B activate tyrosine kinase, promoting oncogenesis. VHL mutations impair pVHL’s role in HIF-1/2 regulation, leading to VEGF overexpression. CWS mutations in PTEN, SDHB, SDHD, and others disrupt cell cycle control and DNA repair.
4. CLINICAL FEATURES¶
MEN1 presents with parathyroid hyperplasia, pancreatic NETs, and pituitary adenomas. MEN2A includes MTC, pheochromocytoma, and parathyroid tumors. MEN2B features MTC, pheochromocytoma, and mucosal neuromas. VHL involves hemangioblastomas, RCC, and pheochromocytoma. NF1 is marked by neurofibromas, café au lait spots, and optic gliomas.
Table 400-3: Biochemical and Radiologic Screening in MEN1¶
| TUMOR | AGE TO BEGIN (YEARS) | BIOCHEMICAL TEST | IMAGING TEST (TIME INTERVAL) |
|---|---|---|---|
| Parathyroid | 8 | Calcium, PTH | None |
| Pancreatic NETs | 20 | Gastrin (± gastric pH) | None |
| Insulinoma | 5 | Fasting glucose, insulin | None |
| Other pancreatic NETs | <10 | Chromogranin A; pancreatic polypeptide, glucagon | MRI, CT, or EUS (annually) |
4.1 Symptomatology¶
Hypercalcemia, hypertension, and endocrine syndromes (e.g., Zollinger-Ellison, Cushing’s) are common. MEN1 patients may have facial angiofibromas, collagenomas, and lipomas. VHL patients develop renal cysts, hemangioblastomas, and pheochromocytoma.
5. DIFFERENTIAL DIAGNOSIS¶
Differential diagnoses include sporadic tumors, other hereditary syndromes (e.g., MEN2, VHL), and non-endocrine conditions. Key features include multiple tumors in different endocrine glands, family history, and genetic testing results.
5.1 Key Differentiators¶
MEN1 vs. MEN2: Parathyroid tumors vs. MTC. VHL vs. NF1: Hemangioblastomas vs. neurofibromas. CWS vs. NF1: Skin pigmentation vs. café au lait spots. Genetic testing is essential for definitive diagnosis.
6. INVESTIGATIONS & DIAGNOSIS¶
Biochemical tests include serum calcium, PTH, gastrin, insulin, and chromogranin A. Imaging uses MRI, CT, and ultrasound. Genetic testing for MEN1, RET, SDH, and VHL mutations is critical. Radionuclide imaging (MIBG, SRS) and PET scans are used for pheochromocytoma and NETs.
Table 400-4: Recommendations for Tests and Surgery in MEN2 and MEN3¶
| RET MUTATION | RISK | RECOMMENDED AGE (YEARS) FOR TEST/INTERVENTION |
|---|---|---|
| Ex8 (533); Ex10 (609, 611, 618, 620); Ex11 (630, 631, 666); Ex13 (768, 790); Ex14 (804); Ex15 (891); Ex16 (912) | + | <3–5 |
| Ex11 (634); Ex15 (883) | ++ | <3 |
| Ex15 (883); Ex16 (918) | +++ | ASAP and by <1 |
6.1 Diagnostic Criteria¶
MEN1: Two or more tumors in parathyroid, pancreas, and pituitary. MEN2A: MTC + pheochromocytoma + parathyroid tumor. VHL: Hemangioblastoma + RCC + pheochromocytoma. Genetic confirmation is required for diagnosis.
7. MANAGEMENT & TREATMENT¶
Surgical resection is the mainstay for tumors (e.g., parathyroidectomy, thyroidectomy). Medical therapies include somatostatin analogs (octreotide, lanreotide), chemotherapy (streptozotocin, 5-FU), and targeted agents (selpercatinib). Radiotherapy and PRRT (177Lu-DOTATATE) are used for metastatic disease.
Table 400-5: HPT-JT Screening Guidelines¶
| TUMOR | TEST | FREQUENCY |
|---|---|---|
| Parathyroid | Serum Ca, PTH | 6–12 months |
| Ossifying jaw fibroma | Panoramic jaw x-ray with neck shielding | 5 years |
| Renal | Abdominal MRI | 5 years |
7.1 Surgical Approaches¶
Total thyroidectomy for MTC in MEN2. Subtotal parathyroidectomy for MEN1. Adrenalectomy for pheochromocytoma. Endoscopic techniques for adrenal-sparing surgery. Central neck dissection for MTC.
8. PROGNOSIS & COMPLICATIONS¶
MEN1 patients have a 50% mortality rate by age 50 due to malignancies. MTC in MEN2 has a 10% mortality rate from early metastases. Complications include hypercalcemia, hypertension, and endocrine syndromes (e.g., Zollinger-Ellison, Cushing’s).
8.1 Survival Rates¶
MEN1: 50% survival at 50 years. MTC: 20% 10-year survival for metastatic cases. VHL: 70% risk of RCC. NF1: 10% risk of optic glioma. CWS: 1–2% risk of thyroid cancer.
9. SPECIAL CONSIDERATIONS¶
Pregnancy in MEN1 requires careful monitoring for hypercalcemia and tumor growth. Pediatric patients may present with early-onset tumors (e.g., parathyroid hyperplasia). Elderly patients face higher risks of complications from surgery and comorbidities.
9.1 Pregnancy Management¶
Avoid calcimimetics during pregnancy. Monitor calcium and PTH levels. Consider prophylactic surgery for pheochromocytoma before pregnancy. Genetic counseling for family planning.
10. KEY POINTS & CLINICAL PEARLS¶
- Genetic testing is essential for diagnosis and family screening. 2. MEN1 requires lifelong biochemical monitoring and imaging. 3. MTC in MEN2 is curable with early thyroidectomy. 4. Targeted therapies (e.g., selpercatinib) improve outcomes for advanced MTC. 5. Multidisciplinary management is critical for complex cases.