The American Joint Committee on Cancer (AJCC)/International Union Against Cancer (UICC) TNM staging Postoperative staging of thyroid cancer can be used to: (1) determine the individual prognosis of patients with differentiated thyroid cancer; (2) guide postoperative adjuvant therapy, including 131I radiotherapy and TSH suppressive therapy, to reduce recurrence and mortality; (3) determine the timing and frequency of follow-up, and provide more intensive follow-up for high-risk patients; and (4) help patients communicate better with their physicians. ③ Determine the timing and frequency of follow-up, and provide more intensive follow-up for high-risk patients; ④ Help patients communicate better with their physicians. The AJCC/UICC classification system based on TNM parameters is applicable to all types of tumors, including thyroid cancer, because it provides an efficient and convenient way to describe the extent of tumors. This classification scheme takes into account many predictors of outcome, the most meaningful of which are the presence of distant metastases, patient age and tumor extent. T1 Tumor diameter ≤2 cm T2 Primary tumor diameter 2-4 cm T3 Primary tumor diameter >4 cm, tumor confined to the thyroid gland or with a small extension outside the thyroid gland T4a Tumor spreads beyond the thyroid envelope and invades subcutaneous soft tissue, larynx, trachea, esophagus or laryngeal nerve T4b Tumor invades the prevertebral fascia or wraps around the carotid artery or mediastinal vessels TX Primary tumor of unknown size, but not extending outside the thyroid gland N0 No lymph node metastasis N1a Tumor metastasis to zone VI [pre-tracheal, paratracheal, and anterior laryngeal (Delphian) lymph nodes] N1b Tumor metastasis to unilateral, bilateral, contralateral cervical, or superior mediastinal lymph nodes NX No intraoperative evaluation of lymph nodes M0 No distant metastases M1 Distant metastases MX No evaluation of distant metastases Staging Patient age <45 years Patient age ≥45 years Stage I Any T, N, and M0 T1,N0,M0 Stage II Any T, N, and 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,M0T3,N1b,M0; T4a,N1b,M0 Stage IVB T4b,any N,M0 Stage IVC Any T,any N,M1 Note: Used with permission from AJCC, originally cited in AJCC Cancer Staging Manual, Sixth Edition (2002)