## MEN 1 Syndrome: Key Features **Key Point:** MEN 1 (Wermer syndrome) is characterized by the "3 P's": **P**arathyroid hyperplasia, **P**ancreatic neuroendocrine tumors, and **P**ituitary adenomas. Medullary thyroid carcinoma is NOT a feature of MEN 1. ### Classic Triad of MEN 1 | Feature | Details | Frequency | |---------|---------|----------| | **Parathyroid hyperplasia** | Primary hyperparathyroidism; most common manifestation | ~95% of patients | | **Pancreatic NET** | Gastrinomas (Zollinger-Ellison syndrome), insulinomas, non-functional tumors | ~70% of patients | | **Pituitary adenomas** | Prolactin-secreting most common; also GH-secreting (acromegaly), non-functional | ~65% of patients | ### Other Associated Tumors in MEN 1 - Adrenocortical tumors (often non-functional) - Carcinoid tumors (thymic, bronchial, gastric) - Cutaneous manifestations: lipomas, collagenomas, angiofibromas - ~~Medullary thyroid carcinoma~~ — **NOT part of MEN 1** **High-Yield:** Medullary thyroid carcinoma (MTC) is the hallmark of **MEN 2A and MEN 2B**, not MEN 1. Both MEN 2 syndromes are caused by RET proto-oncogene mutations, not MENIN mutations. ### MEN 1 vs MEN 2 Comparison | Feature | MEN 1 | MEN 2A | MEN 2B | |---------|-------|--------|--------| | **Gene** | MENIN | RET | RET | | **Medullary thyroid CA** | ✗ | ✓ | ✓ | | **Pheochromocytoma** | ✗ | ✓ | ✓ | | **Primary hyperparathyroidism** | ✓ | ✓ | ✗ | | **Mucosal neuromas** | ✗ | ✗ | ✓ | | **Pituitary adenoma** | ✓ | ✗ | ✗ | **Clinical Pearl:** A patient with medullary thyroid carcinoma should immediately raise suspicion for MEN 2, not MEN 1. RET testing is mandatory in all MTC cases, and family screening is essential. **Mnemonic for MEN 1 — "3 P's":** **P**arathyroid, **P**ancreas, **P**ituitary. Add carcinoid tumors and adrenal tumors as secondary features.
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