Table 3.

TNM classification.

Primary tumour (pT):

TX: Primary tumour cannot be assessed

T0: No evidence of primary tumour

T1: Tumour ≤2 cm in greatest dimension limited to the thyroid

T1a: Tumour ≤1 cm in greatest dimension limited to the thyroid

T1b: Tumour >1 cm but ≤2 cm in greatest dimension limited to the thyroid

T2: Tumour >2 cm but ≤4 cm in greatest dimension limited to the thyroid

T3: Tumour >4 cm limited to the thyroid or gross extrathyroidal extension invading only strap muscles

T3a: Tumour >4 cm limited to the thyroid

T3b: Gross extrathyroidal extension invading only strap muscles (sternohyoid, sternothyroid, thyrohyoid, or omohyoid muscles) from a tumour of any size

T4: Includes gross extrathyroidal extension into major neck structures

T4a: Gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, oesophagus, or recurrent laryngeal nerve from a tumour of any size

T4b: Gross extrathyroidal extension invading prevertebral fascia or encasing carotid artery or mediastinal vessels from a tumour of any size

Regional lymph node (pN):

NX: Regional lymph nodes cannot be assessed

N0: No evidence of regional lymph node metastasis

N0a: One or more cytologic or histologically confirmed benign lymph nodes

N0b: No radiologic or clinical evidence of locoregional lymph node metastasis

N1: Metastasis to regional nodes

N1a: Metastasis to level VI or VII (pretracheal, paratracheal, prelaryngeal/Delphian or upper mediastinal) lymph nodes; this can be unilateral or bilateral disease

N1b: Metastasis to unilateral, bilateral, or contralateral lateral neck lymph nodes (levels I, II, III, IV, or V) or retropharyngeal lymph nodes

Distant metastasis (M):

M0: No distant metastasis

M1: Distant metastasis