## Distinguishing MEN 1 from MEN 2A ### Overview MEN 1 and MEN 2A are distinct hereditary cancer syndromes with overlapping but non-identical component tumours. The key discriminator lies in the **thyroid pathology**. ### Comparison Table | Feature | MEN 1 | MEN 2A | | --- | --- | --- | | **Gene** | MENIN (Chr 11) | RET proto-oncogene (Chr 10) | | **Medullary Thyroid Carcinoma** | Absent | **Present (95%)** | | **Pheochromocytoma** | Absent | Present (50%) | | **Primary Hyperparathyroidism** | Present (90%) | Present (20–30%) | | **Pituitary Adenoma** | Present (30–40%) | Absent | | **Pancreatic/GI Neuroendocrine Tumours** | Present (70%) | Absent | | **Cutaneous Manifestations** | Lipomas, collagenomas, carcinoids | Mucosal neuromas, marfanoid habitus | ### Key Point: **Medullary thyroid carcinoma (MTC)** is the hallmark of MEN 2A and is virtually absent in MEN 1. This is the single best discriminator between the two syndromes. ### Clinical Pearl: **MEN 2A = MTC + Pheo + Hyperparathyroidism** (the "2+1" rule: two endocrine tumours plus one parathyroid disorder). **MEN 1 = "3 P's"**: **P**ancreas, **P**ituitary, **P**arathyroid (plus gastroenteropancreatic neuroendocrine tumours). ### High-Yield: MTC develops in >95% of MEN 2A patients and is often the **earliest and most aggressive** component. Genetic testing for RET mutations is offered to all MEN 2A families, and prophylactic thyroidectomy is recommended in childhood (typically by age 5–10) in RET-positive individuals. ### Mnemonic: **MEN 2 = MTC + Endocrine + Neuroendocrine** - MTC is the signature lesion - MEN 1 lacks MTC entirely [cite:Robbins 10e Ch 24] 
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