Thyroid Cancer Types
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Direct answer
Thyroid cancer has four main histological types, and papillary carcinoma accounts for most cases and has the best prognosis. Papillary and follicular carcinomas are differentiated and respond to radioiodine, with thyroglobulin used for follow-up, whereas medullary carcinoma arises from parafollicular C cells, secretes calcitonin and is treated by surgery. Anaplastic carcinoma is rare, aggressive and does not respond to radioiodine.
What you must remember
- Papillary: Orphan Annie eye nuclei, psammoma bodies and early lymph node spread; BRAF V600E mutation is common.
- Follicular: spreads haematogenously to bone and lung; diagnosis requires capsular or vascular invasion on histology.
- Medullary: calcitonin and CEA are the markers; RET mutations cause MEN 2A, MEN 2B and familial disease.
- Anaplastic: usually older adults with a rapidly enlarging neck mass; very poor prognosis.
- Radioiodine: effective for papillary and follicular carcinoma, not for medullary or anaplastic disease.
- Thyroglobulin: the follow-up marker for differentiated cancers after total thyroidectomy.
- Phaeochromocytoma: must be excluded before thyroid surgery in MEN 2 patients.
Three patients, three types
Three patients with neck masses need different pathways, and the table separates them.
| Feature | 45-year-old woman | 35-year-old man | 78-year-old woman |
|---|---|---|---|
| Presentation | Solitary firm nodule, suspicious on fine needle aspiration | Family history of phaeochromocytoma and thyroid cancer in his father | Rapidly enlarging neck mass with dysphagia and stridor |
| Diagnosis | Papillary carcinoma with nodal metastases | Raised calcitonin and a pathogenic RET mutation, pointing to MEN 2 | Anaplastic carcinoma on histology |
| Treatment | Total thyroidectomy, then radioiodine ablation for the nodal disease | Prophylactic thyroidectomy in childhood or early adulthood, depending on the mutation, after phaeochromocytoma is excluded biochemically | Multidisciplinary care aiming at palliation or symptom control rather than cure |
| Radioiodine and follow-up | Thyroid hormone suppression to a low TSH; follow-up with thyroglobulin and neck ultrasound | Not effective for medullary disease | Not effective |
Papillary carcinoma has the best prognosis, while anaplastic carcinoma has a very poor one. The three cases differ in marker, treatment and prognosis, which is precisely why examiners test the distinction.
Where the exam tries to catch you
Examiners set traps around diagnosis, radioiodine and surgery.
- Trap: diagnosing follicular carcinoma on fine needle aspiration Correct: aspiration cannot distinguish a follicular adenoma from a follicular carcinoma, because the diagnosis depends on capsular or vascular invasion seen on histology.
- Trap: recommending radioiodine for medullary or anaplastic disease Correct: radioiodine is effective only for papillary and follicular carcinoma, which take up iodine.
- Trap: using psammoma bodies alone to diagnose papillary carcinoma Correct: psammoma bodies are not unique to thyroid papillary carcinoma, so examiners look for the combination of nuclear features, including Orphan Annie eye nuclei and nuclear grooves.
- Trap: operating on a MEN 2 patient before excluding phaeochromocytoma Correct: phaeochromocytoma must be excluded before thyroid surgery, because operating on an unrecognised one can be catastrophic.
Frequently asked questions
What histological features define papillary thyroid carcinoma?
Papillary thyroid carcinoma is defined by Orphan Annie eye nuclei, nuclear grooves and psammoma bodies. Lymphatic spread to cervical nodes is typical. Its prognosis is excellent, and it is the most common thyroid cancer type.
Why is follicular thyroid carcinoma diagnosed only on histology?
Follicular thyroid carcinoma is diagnosed only on histology because fine needle aspiration cannot distinguish a follicular adenoma from a follicular carcinoma. Capsular or vascular invasion must be seen on the surgical specimen. This is why follicular neoplasms are often treated surgically before a final diagnosis.
Which marker is used to monitor medullary thyroid carcinoma?
Serum calcitonin is the main marker for medullary thyroid carcinoma, and CEA is used alongside it. Calcitonin levels also help assess the extent of disease and response to treatment. Thyroglobulin is not the marker for this type.
Which thyroid cancer types respond to radioiodine?
Papillary and follicular thyroid carcinomas respond to radioiodine because they take up iodine. Medullary and anaplastic carcinomas do not, so radioiodine is not used for them. This distinction underlies the choice of treatment for each type.
Which hereditary syndrome is linked to medullary thyroid carcinoma?
Medullary thyroid carcinoma is linked to MEN 2A and MEN 2B, which are caused by RET mutations. Phaeochromocytoma and hyperparathyroidism can coexist in these syndromes. Genetic testing for RET is part of the evaluation of affected families.