Follicular Thyroid Carcinoma

🧠 Follicular Thyroid Carcinoma (FTC)

📊 Epidemiology of Follicular Thyroid Carcinoma

• The second most common thyroid carcinoma

• Incidence: 10–15% of all thyroid malignancies.

• Age: Mean = 50 years (6th decade). Rare <30 years.

• Sex: Female : Male = 3 : 1

• Origin: From follicular cells of thyroid.

• Key Difference: Nuclear features of papillary carcinoma are absent.

What are the histopathological features of Papillary Thyroid Carcinoma?

⚠️ Risk Factors of Follicular Thyroid Carcinoma

• Radiation exposure to head/neck.

• Iodine deficiency: More common in iodine-deficient areas (25–40% of thyroid cancers).

• Genetic Mutations

• Syndromic Associations

Which genetic alterations are commonly associated with Follicular Thyroid Carcinoma?

What Familial syndromes are associated with Follicular Thyroid Carcinoma?

🩺 Clinical Features of Follicular Thyroid Carcinoma

Presentation:

• Painless, slow-growing thyroid nodule (cold on scintigraphy).

• Rapid increase in size of a long-standing nodule = malignant change.

Metastasis:

• Lymph node mets: rare (≈4%).

• Distant mets: common (10–15% at presentation).

• Spread: hematogenous

Which are the common sites for distant metastasis in Follicular Thyroid Carcinoma?

🔬 Histology of Follicular Thyroid Carcinoma

WHO 2017 Classification

1. Minimally invasive (most common) – capsular invasion.

2. Encapsulated angioinvasive – vascular invasion <4 vessels.

3. Widely invasive – extensive capsular/vascular invasion ≥4 vessels → aggressive, high mets risk (29–66%).

Macroscopy

• Encapsulated solid lesion with thick capsule.

• Cut section: gray/tan, colloid-filled follicles, fibrosis, calcification, cystic change, hemorrhage.

Microscopy

• Uniform cells; no papillary nuclear features.

• Growth patterns: trabecular, micro/macrofollicular, normofollicular.

• Invasion: capsular, vascular, adjacent thyroid tissue.

• No necrosis, squamous metaplasia, psammoma bodies.

What are the Histological Variants of Follicular Thyroid Carcinoma ?

🧪 Investigations of Follicular Thyroid Carcinoma

• FNAC: Cannot differentiate adenoma vs carcinoma → need histology (capsular/vascular invasion).

• Ultrasound: Solitary, well-defined, iso-/hyperechoic, halo sign, increased internal vascularity.

• Thyroid function test: Often euthyroid, sometimes hyperthyroid.

• X-ray chest: Pulmonary mets.

• CT/MRI: Extent, retrosternal extension.

• Bone scan: For bone metastasis.

💊 Treatment of Follicular Thyroid Carcinoma

1- Surgery

• Hemithyroidectomy: Only if <1 cm, unifocal, no extra-thyroidal spread, no mets.

• Total thyroidectomy (preferred)

What are the indications of Total Thyroidectomy in Follicular Thyroid Carcinoma?

2- Neck Dissection

• Central neck dissection if: tumor >4 cm, extrathyroidal spread, aggressive histology, positive nodes.
• Lateral dissection not routine.

3- Hormone Therapy

• TSH suppression:
  • Thyroxine 2 mcg/kg
  • Liothyronine 20 mcg TDS until histopathology confirmed.

4- Radioiodine Ablation (I-131)

• Only after total thyroidectomy.
• Given 6–8 weeks post-op.

What are the indications of Radioiodine ablation in Follicular Thyroid Carcinoma?

5- External Beam Radiotherapy

• For unresectable, non-radioiodine avid, or recurrent disease.
• IMRT preferred.

📊 Treatment Algorithm

• FNAC = Follicular Neoplasm: → Hemithyroidectomy → If carcinoma → Completion thyroidectomy + RAI.

• FNAC = Follicular Carcinoma: → Direct total thyroidectomy.

• Elderly, >4 cm nodule, FNAC = Follicular Neoplasm: → Total thyroidectomy.

🔎 Treatment Response & Follow-up of Follicular Thyroid Carcinoma

1. Post-RAI Scan: Detects residual/metastatic disease.

2. Stimulated Thyroglobulin (Tg): tumor marker for differentiated thyroid cancer (most sensitive when stimulated)

3. CT Scan: If Tg unreliable or RAI uptake beyond neck.

What are the different response categories while assessing treatment outcome in Follicular Thyroid carcinoma? What is the follow up protocol in each group?

📉 Prognosis of Follicular Thyroid Carcinoma

Poor Prognostic Factors

• Clinical:

  • Age >50
  • Male sex
  • Tumor >4 cm
  • Extrathyroidal extension
  • Distant metastasis at presentation

• Pathological:

  • Vascular/capsular invasion
  • Anaplastic transformation
  • Trabecular growth pattern