1. known distant metastases to lung, bone and other organs 2. intraoperative visualization of tumor breaking through the thyroid envelope and invading subcutaneous soft tissue, larynx, trachea, esophagus, recurrent laryngeal nerve, prevertebral fascia or encircling carotid artery and mediastinal vessels (regardless of tumor size); 3. primary tumor more than 4 cm in diameter. 4. Although the tumor does not breach the thyroid envelope and is between 1-4 cm in diameter, there is proven lymph node metastasis or other intermediate or high risk of recurrence and death. These include: surgical pathology suggestive of microscopic tumor invasion of peri-thyroid soft tissue, highly invasive histologic presentation (e.g., hypercellular, columnar cell, insular cell, diffuse sclerosis, hypofractionated carcinoma, follicular carcinoma, eosinophilic carcinoma, etc.) or vascular invasion, incomplete tumor resection, and hypothyroglobulinemia.