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Table 6. AJCC/UICC TNM Staging: The 8th Ed. TNM
TNM
Category
a
Code Description
Primary tumor
(pT)
TX Primary tumor cannot be assessed
T0 No evidence of primary tumor
T1 Tumor ≤2 cm limited to thyroid
• T1a Tumor ≤1 cm limited to thyroid
• T1b Tumor >1 cm but ≤2 cm limited to thyroid
T2 Tumor >2 cm but ≤4 cm limited to thyroid
T3 Tumor >4 cm or minimal extrathyroidal extension
• T3a Tumor >4 cm limited to thyroid
• T3b Gross extrathyroidal extension to strap muscles
T4 Gross extrathyroidal extension to major neck structures
• T4a Invading so tissue, larynx, trachea, esophagus, or recurrent
laryngeal nerve
• T4b Invading prevertebral fascia or encasing carotid/mediastinal
vessels
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/clinical evidence of 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 present
