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Table 1. Primary Tumor (T)a,b

TXPrimary tumor cannot be assessed.
T0No evidence of primary tumor.
T1Tumor ≤2 cm in greatest dimension limited to the thyroid.
T1aTumor ≤1 cm, limited to the thyroid.
T1bTumor >1 cm but ≤2 cm in greatest dimension, limited to the thyroid.
T2Tumor >2 cm but ≤4 cm in greatest dimension, limited to the thyroid.
T3Tumor >4 cm in greatest dimension limited to the thyroid or any tumor with minimal extrathyroid extension (e.g., extension to sternothyroid muscle or perithyroid soft tissues).
T4aModerately advanced disease.
Tumor of any size extending beyond the thyroid capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve.
T4bVery advanced disease.
Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels.
cT4aIntrathyroidal anaplastic carcinoma.
cT4bAnaplastic carcinoma with gross extrathyroid extension.

aReprinted with permission from AJCC: Thyroid. In: Edge SB, Byrd DR, Compton CC, et al., eds.: AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010, pp 87-96.
bAll categories may be subdivided: (s) solitary tumor and (m) multifocal tumor (the largest determines the classification).
cAll anaplastic carcinomas are considered T4 tumors.