They often derive from more differentiated thyroid cancer or goiter or may follow radiation exposure. The most common complaint is of a growing neck mass. They invade adjacent structures and metastasize extensively to cervical nodes and distant sites. Most are inoperable at time of diagnosis. Lymphocytic thyroiditis and antithyroid antibodies are common.
Primary sarcomas are quite rare.
Angio and fibrosarcomas are the most common. The prognosis is uniformly very poor. The most common metastatic disease to the thyroid is SCCA of the head and neck. In patients who eventually die of thyroid cancer, local recurrence with invasion of vital structures has been shown to be the cause of death most often. Well differentiated thyroid cancer with distant metastases should still undergo local complete control because most of these patients will still die of local disease and I-131 treatment depends on eradication of local tumor.