Differentiated Thyroid Carcinoma (DTC)
Definition
- DTC refers to thyroid cancers that arise from follicular cells and retain some ability to uptake iodine.
- Includes:
- Papillary thyroid carcinoma (PTC) – most common (~80%)
- Follicular thyroid carcinoma (FTC) – ~10–15%
- Hurthle cell carcinoma – less common variant
Epidemiology / Risk Factors
- More common in women (3:1 ratio).
- Peak incidence: 30–50 years old.
- Risk factors: radiation exposure, family history, certain genetic syndromes (e.g., MEN2 not DTC but relevant for thyroid tumors).
Pathophysiology / Molecular Markers
| Marker / Mutation | Relevance |
|---|---|
| BRAF V600E | Common in PTC; associated with aggressive disease and poorer RAI response |
| RAS mutations | More common in FTC; can predict follicular-pattern tumors |
| RET/PTC rearrangements | PTC, especially in radiation-induced cases |
| TERT promoter mutation | Associated with high-risk features and recurrence |
Clinical Features
- Usually presents as a painless thyroid nodule.
- May have cervical lymphadenopathy (more common in PTC).
- Most patients are euthyroid.
Diagnosis
- Ultrasound: evaluate nodule characteristics.
- Fine Needle Aspiration (FNA): cytology for diagnosis (Bethesda system).
- Molecular testing: BRAF, RAS, RET/PTC, TERT (helps prognosis and therapy).
Staging / Risk Stratification
- TNM staging (AJCC 8th edition)
- Risk categories for recurrence: low, intermediate, high (guides adjuvant therapy)
Treatment Overview
- Surgery
- Total thyroidectomy – standard for most DTCs >1 cm, multifocal disease, or high-risk features.
- Lobectomy – selected low-risk patients.
- Radioactive Iodine (RAI, I-131)
- Used for remnant ablation, adjuvant therapy, or metastatic disease.
- Dose depends on risk category and remnant size.
- Thyroid Hormone Suppression Therapy
- Levothyroxine to suppress TSH → reduces tumor stimulation.
- TSH target depends on risk category:
- High-risk: TSH <0.1 mIU/L
- Low-risk: TSH 0.5–2 mIU/L
- Targeted Therapy (for advanced/metastatic DTC)
- Multi-kinase inhibitors (MKIs):
- Lenvatinib, sorafenib – used in RAI-refractory DTC
- BRAF + MEK inhibitors: for BRAF-mutated, RAI-refractory cases
- Multi-kinase inhibitors (MKIs):
Prognosis
- Generally excellent, especially in patients <45 years.
- 10-year survival: ~90–95% overall.
- Poor prognostic factors: older age, distant metastases, aggressive histology, BRAF V600E, TERT promoter mutation.
Pharmacist Pearls
- Monitor thyroid hormone levels and TSH suppression therapy.
- RAI therapy requires radiation safety counseling.
- MKIs (lenvatinib, sorafenib) have toxicities: hypertension, diarrhea, hand–foot syndrome, hepatotoxicity, proteinuria – need close monitoring.
- Molecular testing guides targeted therapy eligibility.