| T1 |
Tumor diameter ≤ 2 cm, limited to the thyroid | T2 |
Primary tumor diameter > 2 cm to 4 cm, limited to the thyroid | T3 |
Primary tumor diameter > 4 cm, limited to the thyroid or with minimal extrathyroidal extension | T4a |
Tumor of any size extends beyond thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve | T4b |
Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels | TX |
Primary tumor size unknown, but without extrathyroidal invasion |
| N0 |
No regional lymph node metastasis | N1a |
Metastasis to level VI (pretracheal, paratracheal, and prelaryngeal/Delphian lymph nodes) | N1b |
Metastasis to unilateral, bilateral, contralateral, cervical, or superior mediastinal lymph nodes | NX |
Nodes not assessed at surgery |
| M0 |
No distant metastases | M1 |
Distant metastases | MX |
Distant metastases not assessed |
| | Patient age < 45 years | Patient age ≥ 45 years |
| Stage I | Any T, any N, M0 | T1, N0, M0 | Stage II | Any T, any N, M1 | T2, N0, M0 | Stage III | | T3, N0, M0 | | T1, N1a, M0 | | T2, N1a, M0 | | T3, N1a, M0 | Stage IVA | | T4a, N0, M0 | | T4a, N1a, M0 | | T1, N1b, M0 | | T2, N1b, M0 | | T3, N1b, M0 | | T4a, N1b, M0 | Stage IVB | | T4b, Any N, M0 | Stage IVC | | Any T, Any N, M1 |
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