Table 2.

AJCC staging, 7th ed., for well-differentiated thyroid cancer based on TNM descriptors [2].

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