Stage IV includes: IVA: (T4a, Any N, M0); (T1-3, N1b, M0); IVB: (T4b, Any N, M0); IVC: (Any T, Any N, M1). T1: Tumor measuring 2 cm or less in greatest dimension limited to the thyroid. T2: Tumor measuring more than 2 cm but less than 4 cm in greatest dimension limited to the thyroid. T3: Tumor measuring 4 cm or more in greatest dimension or with extrathyroidal extension. T4a: Moderately advanced disease; tumor of any size with gross extrathyroidal extension into the nearby tissues of the neck, including subcutaneous soft tissue, larynx, trachea, esophagus, or recurrent laryngeal nerve. T4b: Very advanced disease; tumor of any size with extension towards the spine or into nearby large blood vessels, invading the prevertebral fascia, or encasing the carotid artery or mediastinal vessels. N1b: Metastasis to unilateral, bilateral, or contralateral lateral neck lymph nodes levels I, II, III, IV, or V or retropharyngeal lymph nodes. M0: No distant metastasis. M1: Distant metastasis. (from AJCC 8th Ed.) [from NCI]