Definition of the Primary Tumor (T)

TX—Primary tumor cannot be evaluated

T0—No evidence of primary tumor

T1—Tumor ≥ 2 cm in the largest dimension limited to the thyroid:

T1a—Tumor ≤ 1 cm in the largest dimension limited to the thyroid

T1b—Tumor > 1 cm, but ≤ 2 cm in the largest dimension limited to the thyroid

T2—Tumor > 2 cm, but ≤ 4 cm in the largest dimension limited to the thyroid

T3—Tumor > 4 cm limited to the thyroid or extra gross thyroid extension that invades only the pre-thyroid muscles:

T3a—Tumor > 4 cm limited to the thyroid

T3b—Extra macroscopic thyroid extension that invades only pre-thyroid muscles (sternohyoid, sternothyroid, thyroid or omohyoid muscles) of a tumor of any size

T4—Includes extra gross thyroid extension:

T4a—Extra macroscopic thyroid extension that invades subcutaneous soft tissue, larynx, trachea, esophagus, or recurrent laryngeal nerve of a tumor of any size

T4b—Extra macroscopic thyroid extension that invades the prevertebral fascia, or covers the carotid artery, or mediastinal vessels, of a tumor of any size

Definition of regional lymph nodes (N)

NX—Regional lymph nodes cannot be evaluated

N0—There is no evidence of loco-regional lymph node metastasis:

N0a—One or more benign lymph nodes cytologically or histologically confirmed

N0b—There is no radiological or clinical evidence of regional crazy lymph node metastases

N1—Metastasis to regional nodes:

N1a—Metastasis to lymph nodes of level VI or VII (pretracheal, paratracheal or prelaringeal/Delphiano or upper mediastinal). This may be a unilateral or bilateral disease.

N1b—Metastasis in the lateral, lateral bilateral lymph nodes,

or contralateral (level I, II, III, IV or V), or retropharyngeal lymph nodes

Definition of distant metastasis (M)

M0—No distant metastasis

M1—Remote metastasis