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23rd May 2025
Types and subtypes of thyroid cancers
Thyroid cancers are divided into differentiated and undifferentiated types, as summarised in table 6.
| Cancer type | Age at presentation (years) | Distribution of cases | Pathology | Spread |
|---|---|---|---|---|
| Papillary thyroid carcinoma | 30-50 (~ 44) | >80% | – Differentiated cancer.
– Slow-growing non-encapsulated tumour. The tumour contains complex branching papillae with a fibrovascular core covered by a single layer of tumour cells. – It has a characteristic psammoma body which is a pathognomonic cytoplasmic feature. |
95% of cases the tumour is confined to the neck. 15-20% have local extrathyroidal invasion and 1-2% metastasise via lymphatics. |
| Follicular thyroid carcinoma (FTC) | 40-50 | 10% | – Differentiated cancer.
– It is a neoplasm of thyroid epithelium. It is impossible to differentiate from benign adenoma and FTC. Hence, surgery is usually required for follicular adenoma. – Hürthle cell carcinoma is an aggressive subtype with poor prognosis. |
It shows capsular and vascular invasion. It metastasises 15-20% via haematogenous route to the lungs and bones. |
| Anaplastic thyroid carcinoma | 60-80 | 1-2% | – Undifferentiated cancer.
– Characterized by rapid growth of a firm/hard fixed nodule. |
– It often infiltrates local tissue invading the larynx and great vessels causing stridor and obstructive respiratory symptoms. -It does not move on swallowing. |
| Medullary thyroid carcinoma (MTC) | 50-60 | 5-10% | – Undifferentiated cancer.
– It originates from parafollicular cells (C-cells) |
– It shows tendency to multicentricity, and early lymph node spread. |
| Lymphoma | >40 | – Undifferentiated cancer.
– Associated with autoimmune thyroid disease (Hashimoto’s thyroiditis) – Characterised by rapid enlargement. |
– Maybe limited to thyroid gland or part of systemic non-Hodgkin lymphoma. | |
| Hürthle cell carcinoma (HCC) | 3-4% | – A variant of follicular thyroid tumours. It shows classical cytology appearance of large cells with abundant eosinophilic granular cytoplasm and large hyperchromatic nuclei and prominent nucleoli. | – It shows capsular and vascular invasion, lymph node or distant metastasis. |
Table 6: Thyroid cancer types overview
TNM staging of thyroid cancer for papillary and follicular thyroid carcinoma
Thyroid cancer is classified according to size and extent of the tumour (T), regional LN involvement (N), and the distant metastasis (M).
- T1 is tumour size ≤2 cm and limited to the thyroid.
- T2 is tumour size >2cm but ≤4cm and limited to the gland.
- T3 is tumour size >4cm limited to the thyroid or any tumour with minimal extrathyroidal invasion.
- T4 is subdivided into T4a and T4b where tumour can be of any size and invading structures beyond thyroid capsule.
- N0 has no regional lymph node metastasis; N1/N2 suggests lymph node involvement
- M0 denotes no distant metastasis present; M1 denotes presence of distant metastasis.
The eighth edition for TNM staging for differentiated thyroid carcinoma depends on the cut-off age of 55 years old.
- Patients of age <55 years old, cancer can be subdivided into:
- Stage I (with M0)
- Stage II (with M1).
- Patients ≥55 years old, thyroid carcinoma is subdivided to 4 stages:
- Stage I (T1 or T2 with N0 and M0)
- Stage II (T1+N1+M0 or T1+N1+M0 or T3+N0/N1+M0)
- Stage III (T4a+N0/N1+M0)
- Stage 4 (T4b+N0/N1+M0 or any T+ any N +M1
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