Thyroid anaplastic carcinoma transformed from papillary carcinoma in extrathyroid area.

We report a 75-year-old male with anaplastic carcinoma in an extrathyroid area. Thyroid remained unchanged. The patient is alive without incident of tumor recurrence at 3.5 years after total resection and at 5 years after initial symptom. The tumor developed between the sternocleidomastoid muscle and common carotid artery, and was completely separated from the thyroid. The tumor location was consistent with a branchial cyst. The tumor consisted of two parts; an upper solid tumor and a deep cystic tumor. The former showed anaplastic carcinoma with osteoclast-like giant cells. The latter was consistent with thyroid papillary carcinoma. The center was intermingled with these two carcinomas. Anaplastic carcinoma cells were positive for vimentin and papillary carcinoma cells were positive for keratin, thyroglobulin, and thyroid transcription factor-1. These results remain insufficient to find any conclusions concerning the tumor nature; either ectopic thyroid carcinoma arising from a branchial cyst or occult thyroid carcinoma metastasis. This is rare case in which thyroid anaplastic carcinoma transformed from papillary carcinoma in an extrathyroid area.