Age <55 years, any T, any N, M0 - stage 1 Any T, any N, M 1 - stage 2 Primary tumor (T) Tx = Primary tumor cannot be assessed T0 = No evidence of primary tumor T1 = Tumor <= 2cm in greatest dimension limited to the thyroid T1a = Tumor <= 1 cm in greatest dimension limited to the thyroid T1b = Tumor >1cm but <= 2 cm in greatest dimension limited to the thyroid T2 = Tumor >2cm but <= 4 cm in greatest dimension limited to the thyroid T3 = Tumor >4 cm limited to the thyroid, or gross extrathyroidal extension invading only strap muscles T3a = Tumor >4cm limited to the thyroid T3b = Gross extrathyroidal extension invading only strap muscles (sternohyoid, sternothyroid, thyrohyoid or omohyoid muscles) from a tumor of any size T4 = Includes gross extrathyroidal extension beyond the strap muscles T4a = Gross extrathyroidal extension invading subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve from a tumor of any size T4b = Gross extrathyroidal extension invading preveebral or encasing the aery or mediastinal Vessels from a tumor of any size Regional lymph nodes (N) NX = Regional lymph nodes cannot be assessed N0 = No evidence of locoregional lymph node metastasis N0a = One or more cytologically or histologically confirmed benign lymph nodes N0b = No radiologic or clinical evidence of locoregional lymph node metastasis N1= Metastasis to regional nodes N1a = Metastasis to level VI or VII (pretracheal, paratracheal, or prelaryngeal/ Delphian, or upper Mediastinal) lymph nodes. This can be unilateral or bilateral disease. N1b = Metastasis to unilateral, bilateral, or contralateral lateral neck lymph (levels I, II, III, IV, or V) or retropharyngeal lymph nodes Distant Metastasis (M) M0 = No distant metastasis M1 = Distant metastasis