Define Thyroid Carcinoma. Describe its types, clinical features, investigations and management.

The Concept — Classify BY Cell of Origin & Behaviour

Thyroid cancers are best understood by their cell of origin, because this determines their behaviour, spread, prognosis and treatment. Most arise from the hormone-producing follicular cells and are called 'differentiated' (papillary and follicular) — these behave well. A distinct group arises from the calcitonin-producing parafollicular C cells (medullary carcinoma), and a rare, lethal group is undifferentiated (anaplastic). Holding this classification in mind makes the whole topic coherent.

The Types

A rare thyroid lymphoma can also arise, characteristically in a gland affected by Hashimoto's thyroiditis.

Clinical Features

Most present as a thyroid nodule or swelling, sometimes with features of malignancy — a hard fixed lump, cervical lymphadenopathy, hoarseness (recurrent laryngeal nerve involvement), or dysphagia. Anaplastic carcinoma presents dramatically with a rapidly enlarging hard mass causing stridor, dysphagia and hoarseness from local invasion. Medullary carcinoma may additionally cause flushing and diarrhoea (from calcitonin and other secreted peptides).

Investigations

The nodule is assessed by ultrasound and FNAC with thyroid function tests. For suspected medullary carcinoma, serum calcitonin is a tumour marker, and — critically — the patient is screened for men 2 and an associated phaeochromocytoma (plasma/urinary metanephrines) must be excluded and treated before any thyroid surgery, to avoid a hypertensive crisis on the table.

Management

• Differentiated (papillary/follicular) — total thyroidectomy (hemithyroidectomy for small, low-risk papillary tumours), with neck dissection for involved nodes; radioiodine (I-131) ablation of residual/metastatic thyroid tissue; lifelong thyroxine to suppress TSH (removing the growth stimulus); and serum thyroglobulin as a follow-up marker of recurrence.
• Medullary — total thyroidectomy with central compartment node dissection; it does not take up iodine, so radioiodine is ineffective; follow up with calcitonin.
• Anaplastic — usually palliative (airway protection/tracheostomy, external radiotherapy, chemotherapy), as cure is rarely possible.

Staging & Prognostic Factors

Prognosis in differentiated cancer depends less on the tumour type than on patient and tumour factors captured in scoring systems (such as AMES/ages): Age (older patients do worse), Metastases, Extent of the primary/extrathyroidal spread, and Size. This is why a young woman with node-positive papillary cancer still has an excellent outlook, whereas the same histology in an older patient with extrathyroidal extension is treated far more aggressively.

Follow-up & Recurrence

After treatment of differentiated cancer, follow-up exploits the biology: having removed all normal thyroid tissue, any detectable serum thyroglobulin (or a rising level) signals recurrent or residual tumour, and whole-body radioiodine scans can localise it. For medullary cancer the equivalent markers are calcitonin and CEA. Lifelong follow-up is standard because differentiated cancers can recur years later, and recurrence is often still curable.

Management of Advanced & Recurrent Disease

Advanced differentiated cancer with distant metastases is still often treatable because the tissue may take up radioiodine: metastases in bone or lung can be targeted with therapeutic I-131 after total thyroidectomy, alongside TSH-suppressive thyroxine. Where tumours dedifferentiate and lose iodine avidity, or in progressive medullary and anaplastic disease, newer targeted kinase inhibitors (e.g. Against the RET or BRAF pathways) have a role. External-beam radiotherapy is used for unresectable or symptomatic local disease. The overarching principle is that differentiated thyroid cancer, even when advanced, frequently follows an indolent course and is managed with a long-term outlook.

A Note on Presentation Via Nodes

An important clinical pearl is that differentiated thyroid cancer, especially papillary, may first present as a lateral cervical lymph node rather than a thyroid lump — a firm neck node in a young adult should prompt assessment of the thyroid. Conversely, the finding of thyroid cancer mandates careful assessment of the neck nodal levels, because nodal disease guides the extent of surgery. This bidirectional relationship between the gland and the neck nodes is central to planning the correct operation.

• Differentiated cancer: total thyroidectomy + radioiodine ablation + TSH-suppressive thyroxine; thyroglobulin as marker.
• Medullary: total thyroidectomy + central node dissection; calcitonin marker; NO radioiodine.
• Exclude phaeochromocytoma before medullary/men thyroid surgery.

Papillary spreads by lymphatics; follicular by blood.

• Classify by origin: differentiated (papillary, follicular — follicular cells), medullary (C cells), anaplastic (undifferentiated), lymphoma (Hashimoto's).
• Papillary (commonest, young, lymphatic spread, excellent prognosis); follicular (blood spread to bone/lung, needs histology).
• Medullary: secretes calcitonin, sporadic or men 2 (RET) — screen for phaeochromocytoma first; anaplastic: elderly, rapidly fatal.
• Differentiated → total thyroidectomy + radioiodine + TSH suppression + thyroglobulin follow-up.
• Medullary → total thyroidectomy + central node dissection, no radioiodine; anaplastic → palliative.