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 |