8th edition of the TNM classification for the thyroid by the UICC (Union for International Cancer Control), valid and binding worldwide from January 2018. It is identical to the 8th edition of the TNM classification of the American Joint Committee on Cancer (AJCC) published in 2017.
It includes specific staging for:
- Differentiated thyroid carcinomas (PTC, FTC)
- Medullary carcinomas (MTC)
- Anaplastic carcinomas (ATC)
TNM classification thyroid
T category: Tumor size and local spread
Stage |
|
|---|---|
T1a | Tumor ≤ 1 cm, confined to the thyroid |
T1b | Tumor > 1 cm to ≤ 2 cm, confined to the thyroid |
T2 | Tumor > 2 cm to ≤ 4 cm, confined to the thyroid |
T3a | Tumor > 4 cm, confined to the thyroid |
T3b | Tumor of any size with macroscopic invasion into infrahyoid muscles |
T4a | Invasion into subcutaneous tissue, larynx, trachea, esophagus, or recurrent laryngeal nerve |
T4b | Invasion into prevertebral fascia, major vessels, or mediastinal structures |
Note: Microscopic extrathyroidal extension (minimal ETE) no longer automatically leads to T3, as in previous editions.
N category: Lymph node metastases
Stage | |
|---|---|
N0 | No clinically or histologically proven regional lymph node metastases |
N1a | Metastases in central lymph nodes (Level VI or Level VII – e.g., pretracheal, paratracheal, prelaryngeal) |
N1b | Metastases in lateral cervical lymph nodes (Level I–V) or in the upper mediastinum |
M category: Distant metastases
M0 | No distant metastases |
M1 | Distant metastases present (e.g., lung, bone) |
Important feature: Age-dependent staging for differentiated thyroid carcinomas at the time of diagnosis:
Patients <55 years |
|
|---|---|
Stage I | T1 – T4, N0 or N1, M0 |
Stage II | Any T/N combination with M1 |
➤ Lymph node involvement does not worsen the stage in patients < 55 years, only distant metastases (M1) lead to Stage II.
Patients ≥55 years |
|
|---|---|
Stage I | T1 – T2, N0, M0 |
Stage II | T1 – T2 with N1 or T3 with any N, M0 |
Stage III | T4a with any N, M0 |
Stage IV | T4b or any T/N combination with M1 |
The medullary thyroid carcinoma (MTC) is also classified according to the TNM system of the UICC (8th edition) – separately from differentiated thyroid carcinomas (DTC), as it behaves biologically and clinically fundamentally differently (e.g., no radioiodine uptake, different metastasis pathway, tumor markers: Calcitonin and CEA).
Staging of MTC (identical for all age groups, unlike DTC there is no age-dependent staging)
Stage | TNM combination |
|---|---|
Stage I | T1, N0, M0 |
Stage II | T2 – T3, N0, M0 |
Stage III | T1 – T3 with N1a, M0 |
Stage IVa | T4a or N1b, M0 |
Stage IVb | T4b, any N, M0 |
Stage IVc | M1, regardless of T/N |
Special features of MTC
- Tumor markers: Calcitonin and CEA are crucial for diagnosis, assessment of progression, and postoperative monitoring
- No radioiodine uptake → no radioiodine therapy possible
- Early lymphatic metastasis
- Can occur sporadically or familial (RET mutation / MEN2) → genetic screening recommended
The anaplastic thyroid carcinoma (ATC) is a highly aggressive, undifferentiated tumor with an extremely poor prognosis.
In the UICC TNM classification (8th edition), ATC has its own classification, which considers its particularly poor biology and prognosis.
Anaplastic thyroid carcinoma is always classified as Stage IV, as the disease is generally considered highly malignant.
The TNM subdivision into IV A, IV B, IV C serves to differentiate between localized, inoperable, and metastatic disease.
TNM classification for anaplastic thyroid carcinoma (ATC)
T category (local spread)
T4a | Tumor infiltrates subcutaneous tissue, larynx, trachea, esophagus, or recurrent nerve |
T4b | Tumor infiltrates spine, major vessels (e.g., carotid artery) or mediastinal structures |
N category (lymph node involvement)
N0 | No regional lymph node involvement |
N1 | Metastases in central or lateral neck lymph nodes or in the upper mediastinum |
M category (distant metastases)
M0 | No distant metastases |
M1 | Distant metastases present (e.g., lung, bone, brain, etc.) |
Staging: ALWAYS Stage IV
Stage IVa | T4a, N0 or N1, M0 | Locally infiltrative, possibly still resectable |
Stage IVb | T4b, any N, M0 | Invasion into unresectable structures (e.g., major vessels) |
| Stage IVc | any T/N combination with M1 | Metastatic disease – usually palliative |
Clinical significance
- ATC is a medical emergency: rapid tumor growth, early infiltration of trachea/esophagus, high mortality
- Prognosis even in Stage IVa is limited: median survival 6 – 12 months
- Multimodal therapy necessary: surgery (if possible) + radiochemotherapy ± targeted therapy (e.g., in BRAF-V600E mutation)