Differences between papillary, follicular, medullary thyroid carcinoma
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Differences Between Papillary, Follicular, and Medullary Thyroid Carcinoma
Here is a comprehensive comparison across all major dimensions.
1. Cell of Origin
| Feature | Papillary (PTC) | Follicular (FTC) | Medullary (MTC) |
|---|---|---|---|
| Cell of origin | Follicular epithelial cells | Follicular epithelial cells | Parafollicular C cells (neuroendocrine) |
| Hormone produced | None (nonfunctional) | Rarely hyperfunctional | Calcitonin (+ somatostatin, serotonin, VIP) |
MTC is fundamentally different from PTC and FTC - it arises from C cells, not follicular epithelium, and is therefore a neuroendocrine tumor.
2. Epidemiology
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Frequency | Most common (~80% of thyroid cancers) | ~10-15% | ~5% |
| Peak age | Any age; commonest in 30s-40s | 40-60 years | Sporadic: 5th-6th decade; familial: younger, including children |
| Sex ratio | F > M | F > M (3:1) | Similar, slightly F > M |
| Familial | Rare | Rare | 30% familial (MEN 2A, MEN 2B, familial MTC) |
3. Risk Factors
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Ionizing radiation | Strong risk factor (esp. childhood) | Less association | No |
| Iodine deficiency | No significant link | More common in iodine-deficient areas | No |
| Genetic predisposition | RET/PTC rearrangements in radiation-associated | PAX8-PPARG rearrangement | Germline RET mutation (MEN 2A/2B) |
4. Molecular Genetics
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Key mutation | BRAF V600E (40-65%); RET/PTC rearrangements (10-20%); RAS (10-30%) | RAS mutations; PAX8-PPARG fusion t(2;3); PIK3CA gain-of-function; PTEN loss | RET point mutations (germline in familial; somatic in ~50% sporadic) |
| Pathway | MAPK pathway | PI3K/AKT pathway | RET tyrosine kinase constitutive activation |
All three mutations in PTC (BRAF, RET, RAS) are mutually exclusive since they have redundant effects on the MAPK pathway. - Robbins & Kumar Basic Pathology, p. 736
5. Gross and Microscopic Morphology
Papillary Thyroid Carcinoma
- Solitary or multifocal; may be encapsulated or infiltrative
- Branching papillae with fibrovascular stalks
- Hallmark nuclei: "ground-glass" / "Orphan Annie eye" nuclei (optically clear, empty chromatin), nuclear grooves, and pseudo-inclusions
- Psammoma bodies (concentrically calcified structures) - essentially pathognomonic; almost never seen in FTC or MTC
- Lymphatic invasion common; lymph node metastases in up to 50%
Follicular Thyroid Carcinoma
- Single nodule; may look grossly identical to a follicular adenoma
- Uniform cells forming small follicles resembling normal thyroid
- No psammoma bodies, no papillary nuclear features
- Diagnosis requires demonstration of capsular invasion and/or vascular invasion - extensive histologic sampling required
- Hematogenous spread to lungs, bone, liver (NOT lymph nodes typically)
Medullary Thyroid Carcinoma
- Solitary (sporadic) or bilateral/multicentric (familial)
- Polygonal to spindle-shaped cells in nests, trabeculae, or gland-like structures
- Amyloid deposits in the stroma (derived from altered calcitonin) - distinctive feature
- Multicentric C-cell hyperplasia in surrounding parenchyma is characteristic of familial cases (precursor lesion)
- Calcitonin demonstrable by immunohistochemistry in tumor cells and amyloid
6. Spread Pattern
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Lymphatic spread | Common (up to 50% cervical nodes) | Uncommon | Common - central and lateral neck nodes |
| Hematogenous spread | Uncommon | Common - lungs, bone, liver | Can occur (hepatic, skeletal) |
| Bilateral | Can be multifocal | Usually unilateral | Bilateral in familial cases |
7. Tumor Marker
| PTC | FTC | MTC |
|---|---|---|
| Thyroglobulin (post-op surveillance) | Thyroglobulin (post-op surveillance) | Calcitonin (diagnosis + post-op follow-up); CEA also elevated |
Calcitonin measurement is central to MTC diagnosis and follow-up. Elevated serum calcitonin provides a marker of residual or recurrent disease. - Harrison's Principles of Internal Medicine 22E
8. Radioiodine (RAI) Uptake
| PTC | FTC | MTC |
|---|---|---|
| Yes (if well-differentiated) | Yes (well-differentiated metastases may take up RAI - useful for ablation) | No - MTC does not arise from follicular cells, so no RAI uptake |
9. Clinical Presentation
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Presentation | Painless neck mass; incidental on imaging | Solitary cold nodule | Neck mass ± compressive symptoms (dysphagia, hoarseness) |
| Paraneoplastic | None | Rarely hyperfunctional | Diarrhea (VIP secretion); Cushing's syndrome (ACTH) |
| Association | Prior radiation | Iodine deficiency, goiter | MEN 2A (pheo + hyperparathyroidism), MEN 2B (pheo + mucosal neuromas + marfanoid habitus) |
10. Prognosis
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| 10-year survival | >95% (excellent) | Minimally invasive: >90%; Widely invasive: ~50% | Sporadic: ~80% if localized; metastatic: ~20% at 10 years |
| Lymph node mets effect | Isolated nodal mets do NOT significantly worsen prognosis | Rare; less impact | Significant prognostic impact |
| Overall | Most indolent | Intermediate | More aggressive than PTC/FTC |
11. Treatment
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Surgery | Total thyroidectomy ± lymph node dissection | Total thyroidectomy | Total thyroidectomy + central neck dissection (bilateral central if evident MTC) |
| Radioiodine | Yes (post-op ablation) | Yes (well-differentiated metastases) | Not used |
| TSH suppression | Yes (levothyroxine) | Yes | Not applicable |
| Targeted therapy | BRAF inhibitors (for BRAF-mutated advanced disease) | None established | Vandetanib, cabozantinib, selpercatinib (most selective RET inhibitor) for advanced/metastatic disease |
| Prophylactic thyroidectomy | Not applicable | Not applicable | Offered to RET mutation carriers (age <1-5 years depending on mutation risk) |
| Screening family members | Not routine | Not routine | Mandatory - RET genetic testing + calcitonin screening |
Quick Summary Table
| Feature | PTC | FTC | MTC |
|---|---|---|---|
| Origin | Follicular epithelium | Follicular epithelium | C cells (neuroendocrine) |
| Frequency | 80% | 10-15% | 5% |
| Key mutation | BRAF V600E | RAS, PAX8-PPARG | RET |
| Nuclear hallmark | Ground-glass nuclei, grooves, pseudo-inclusions | None (follicular pattern) | N/A |
| Psammoma bodies | Yes | No | No |
| Amyloid stroma | No | No | Yes |
| Tumor marker | Thyroglobulin | Thyroglobulin | Calcitonin |
| RAI uptake | Yes | Yes | No |
| Metastasis route | Lymphatic (cervical nodes) | Hematogenous (lung, bone) | Both |
| Familial | Rare | Rare | 30% (MEN 2A/2B) |
| Prognosis | Excellent (>95% 10-yr) | Intermediate | Worse (20% at 10yr if metastatic) |
Sources: Robbins & Kumar Basic Pathology, pp. 735-740; Harrison's Principles of Internal Medicine 22E, pp. 767-771, 3129; Quick Compendium of Clinical Pathology 5th ed., p. 415
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