Thyroid Cancer
Summary
Thyroid cancer is the most common endocrine malignancy. The incidence is rising (partly due to better detection of small nodules). The vast majority are Differentiated Thyroid Cancers (Papillary and Follicular), which have an excellent prognosis (>90% 10-year survival). Anaplastic carcinoma is rare but universally fatal. Medullary carcinoma arises from C-cells and may be part of MEN2 syndrome. [1,2]
Classification (The "Big 4")
- Papillary (80%): Young females (30-50). Slow growing. Spreads via Lymphatics to cervical nodes. Prognosis Excellent.
- Follicular (10%): Older (40-60). Iodine deficiency areas. Spreads via Blood (Haematogenous) to bone/lungs. Prognosis Good.
- Medullary (5%): Neuroendocrine tumour of Parafollicular C-Cells. Secretes Calcitonin. Associated with MEN2. Prognosis Variable.
- Anaplastic (less than 2%): Elderly (>70). Undifferentiated. Aggressive local invasion. Prognosis Dismal (months).
Clinical Pearls
The "Follicular Dilemma": You CANNOT diagnose Follicular Cancer on FNA cytology alone. FNA shows "Follicular cells", but benign adenomas also look like this. The definition of carcinoma requires Capsular or Vascular Invasion, which can only be seen on histology after removing the lump (diagnostic hemithyroidectomy).
Orphan Annie Eyes: The classic histological appearance of Papillary Cancer nuclei (optically clear, ground-glass). Also Psammoma bodies (calcific laminations).
TSH Suppression: Thyroid cells (and cancer cells) grow in response to TSH. After thyroidectomy, we give high-dose Levothyroxine to suppress TSH to less than 0.1 mU/L, starving any remaining cancer cells of their growth signal.
Demographics
- Gender: Female > Male (3:1).
- Age: Bimodal. Papillary (young), Anaplastic (old).
- Risk Factors: Ionizing Radiation (Chernobyl, childhood neck X-rays), Family History (MEN2, FAP).
Molecular Genetics
- Papillary: BRAF V600E mutation (45%), RET/PTC rearrangement.
- Follicular: RAS mutation, PAX8-PPARy.
- Medullary: RET Proto-oncogene mutation (Germline in MEN2, Somatic in sporadic).
Symptoms
Signs
- Neck Exam: From behind. Ask patient to swallow water.
- Pemberton's Sign: Retrosternal goitre causing SVC obstruction.
- Vocal Cords: Flexible Nasendoscopy (FNE) to check mobility pre-op.
1. Ultrasound (U Scale)
- U1/2: Benign / Cystic.
- U3/4/5: Solid, Hypoechoic, Microcalcifications, Irregular margins. (Suspicious).
2. Fine Needle Aspiration (FNA)
- Thy1: Non-diagnostic.
- Thy2: Benign.
- Thy3: Indeterminate ("Follicular Lesion"). Needs excision.
- Thy4/5: Malignant.
3. Bloods
- TFTs: Usually normal (Euthyroid).
- Calcitonin: If Medullary suspected or MEN2 family history.
- Thyroglobulin: NOT diagnostic (raised in all goitres), but used for Monitoring post-op.
Management Algorithm
SUSPICIOUS THYROID NODULE
↓
ULTRASOUND
┌───────────┴───────────┐
BENIGN (U2) SUSPICIOUS (U3-5)
↓ ↓
DISCHARGE FNA
┌───────────┴───────────┐
THY3 (Follicular) THY4/5 (Papillary)
↓ ↓
DIAGNOSTIC SURGERY DEFINITIVE SURGERY
(Hemithyroidectomy) (Total / Hemi)
+ Frozen Section ↓
↓ + NECK DISSECTION
CANCER CONFIRMED? (if nodes +ve)
YES -> Completion ↓
NO -> Stop RADIOIODINE (RAI)
(For high risk)
↓
TSH SUPPRESSION
Surgical Options
- Hemithyroidectomy: For small (less than 1cm) low-risk cancers or diagnostic for Thy3.
- Total Thyroidectomy: For >1cm cancers/multifocal.
- Neck Dissection: If lymph nodes involved.
Adjuvant Therapy
- Radioactive Iodine (RAI - I-131):
- Patient swallows a capsule of radioactive iodine.
- Thyroid cells (including metastases) take it up avidly and are destroyed from the inside.
- Patient must be isolated for a few days (radioactive).
- Levothyroxine: Lifelong. Dosed to suppress TSH (Target less than 0.1).
Surgical Risks
- Recurrent Laryngeal Nerve Injury: Hoarse, breathy voice. Bilateral injury = Airway obstruction (tracheostomy).
- Hypocalcaemia: Damage to Parathyroid glands (transient in 20%, permanent in 2%). Causes tetany perioral tingling.
Disease Sequelae
- Bone Mets: Follicular cancer prefers bone (pulsatile masses).
- Lung Mets: "Cannonball" metastases.
- Papillary/Follicular: Excellent. 20-year survival >90%.
- Medullary: Variable. 10-year survival ~75%.
- Anaplastic: less than 1 year median survival.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Thyroid Cancer | British Thyroid Assoc (BTA) | U-grading for US. Thy-grading for FNA. |
| Nodule Mgmt | ATA (American Thyroid Assoc) | Thresholds for biopsy size. |
Landmark Evidence
1. TSH Suppression
- Meta-analyses confirm that keeping TSH less than 0.1 significantly reduces recurrence in high-risk DTC patients.
What is it?
A cancer starting in the hormone-producing cells of the thyroid gland in the neck.
Is it curable?
Yes, highly curable. Most patients are young and go on to live a normal lifespan. It is often called the "good cancer" (though no cancer is truly good).
How is it treated?
Usually, we remove the whole thyroid gland. Afterward, you might swallow a radioactive pill to "mop up" any microscopic cells left behind.
Will I need tablets?
Yes. Without a thyroid, you need to take thyroxine hormone replacement every day for the rest of your life. We give you a slightly higher dose to switch off your brain's signal (TSH) which stops the cancer coming back.
Primary Sources
- Perros P, et al. Guidelines for the management of thyroid cancer. British Thyroid Association. 2014.
- Haugen BR, et al. 2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer. Thyroid. 2016.
Common Exam Questions
- Pathology: "Orphan Annie Eyes?"
- Answer: Papillary Carcinoma.
- Diagnosis: "How to confirm Follicular Cancer?"
- Answer: Excision Biopsy (needs capsular invasion). FNA cannot distinguish from adenoma.
- Complication: "Tingling lips post-thyroidectomy?"
- Answer: Hypocalcaemia (Parathyroid damage). Check Calcium.
- Marker: "Blood test to monitor recurrence?"
- Answer: Thyroglobulin. (Should be usually undetectable after total thyroidectomy).
Viva Points
- Medullary Carcinoma Management: Does RAI work? NO. C-cells do not take up iodine. Treatment is surgery. Screen for Phaeochromocytoma (MEN2) before surgery to avoid hypertensive crisis.
- Anaplastic: Why is it so hard? It invades the trachea/carotids rapidly. Tracheostomy often needed for airway. Palliative chemo/radio used.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.