Stage IV includes: IVA (T4a, N0, M0); (T4a, N1a, M0); (T1, N1b, M0); (T2, N1b, M0); (T3, N1b, M0); (T4a, N1b, M0); IVB (T4b, Any N, M0); IVC (Any T, Any N, M1). T4a: Moderately advanced local disease. Tumor of any size extending beyond the thyroid gland capsule to invade subcutaneous soft tissues, larynx, trachea, esophagus, or recurrent laryngeal nerve. T1: Tumor size 2 cm or less in greatest dimension, limited to the thyroid gland. T2: Tumor more than 2 cm but not more than 4 cm in greatest dimension, limited to the thyroid gland. T3: Tumor more than 4 cm in greatest dimension and limited to the thyroid gland, or tumor of any size with minimal extrathyroid extension (e.g., extension to sternothyroid muscle or perithyroid soft tissues). T4b: Very advanced disease. Tumor invades prevertebral fascia or encases carotid artery or mediastinal vessels. N0: No regional lymph node metastasis. N1a: Metastasis to pretracheal, paratracheal or prelaryngeal/Delphian lymph nodes (Level VI lymph nodes). N1b: Metastasis to unilateral, bilateral or contralateral cervical (Levels I, II, III, IV, or V) or retropharyngeal or superior mediastinal lymph nodes (Level VII). M0: No distant metastasis. M1: Distant metastasis. (AJCC 7th ed.) [from NCI]