Multiple endocrine neoplasia (MEN) type IIa, also known as Sipple syndrome, accounts for most cases of MEN II and is characterised by:
- pheochromocytomas: in 50% of patients, often bilateral, and can be extra-adrenal
- medullary thyroid cancer: 100% of patients, aggressive, and may secrete calcitonin
- parathyroid hyperplasia: only seen in 20% of patients, and often presents with hypercalcaemia and renal calculi
A small proportion of individuals have a RET 631 proto-oncogene mutation.
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