Write a short note on Medullary Carcinoma & MEN Syndromes.

The Concept

Medullary thyroid carcinoma (MTC) is distinct from the other thyroid cancers because it does not arise from the hormone-making follicular cells but from the parafollicular 'C' cells, which normally secrete calcitonin. This origin explains its two defining features: it produces calcitonin as a tumour marker, and it does not take up iodine (so radioiodine is useless). About 25% of cases are hereditary, occurring as part of the men 2 syndromes through mutations in the RET proto-oncogene.

The Men 2 Syndromes

Multiple Endocrine Neoplasia type 2 is an autosomal-dominant syndrome you must know:

• Men 2A = medullary thyroid carcinoma + phaeochromocytoma + primary hyperparathyroidism.
• Men 2B = medullary thyroid carcinoma + phaeochromocytoma + mucosal neuromas + a marfanoid habitus (no hyperparathyroidism).

(For completeness, men 1 is a different syndrome — parathyroid, pancreatic and pituitary tumours.)

Clinical Features & Management

MTC presents as a thyroid nodule, often with cervical nodes, and may cause flushing and diarrhoea from secreted peptides. Before any surgery it is essential to screen for and treat a coexisting phaeochromocytoma (plasma/urinary metanephrines), because operating on an unrecognised phaeo can precipitate a fatal hypertensive crisis. Treatment is total thyroidectomy with central compartment lymph-node dissection; because it does not concentrate iodine, radioiodine is not used, and calcitonin (and CEA) are followed as markers. Relatives are offered RET genetic testing, and gene-positive family members are offered prophylactic thyroidectomy.

Screening & Prophylaxis

Because MTC in men 2 is driven by a defined RET mutation, family screening is genetic: relatives are offered RET testing, and gene-positive individuals are offered prophylactic total thyroidectomy — often in childhood — before cancer develops, one of the clearest examples of gene-directed preventive surgery. Lifelong biochemical surveillance (calcitonin/CEA) detects recurrence, and coexisting phaeochromocytoma and hyperparathyroidism are monitored for.

Clinical & Genetic Implications

Because a quarter of MTC is hereditary, the diagnosis has implications for the whole family. Every patient with MTC is offered RET genetic testing; if positive, relatives are tested, and gene carriers are offered prophylactic thyroidectomy (timed by the specific mutation's risk, sometimes in early childhood). Before any surgery, a coexisting phaeochromocytoma is excluded and treated first, and primary hyperparathyroidism is sought in men 2A. This makes MTC a model of how a single tumour diagnosis triggers genetic counselling, family screening and preventive surgery.

The Bottom Line

The practical clinical message is that MTC turns a thyroid operation into a genetic and endocrine event: it mandates pre-operative exclusion of phaeochromocytoma, calcitonin/CEA follow-up, RET testing and family screening, and consideration of prophylactic thyroidectomy in gene carriers — a breadth of implications quite unlike the differentiated cancers, and the reason it is so frequently examined.

Screen for phaeochromocytoma before operating on men 2.

• MTC arises from parafollicular C cells → secretes calcitonin (marker); does not take up iodine.
• ~25% hereditary, part of men 2 (RET proto-oncogene, autosomal dominant).
• Men 2A = MTC + phaeochromocytoma + hyperparathyroidism; men 2B = MTC + phaeo + mucosal neuromas + marfanoid habitus.
• Exclude/treat phaeochromocytoma before thyroid surgery.
• Total thyroidectomy + central node dissection (no radioiodine); calcitonin follow-up; RET testing for relatives.