Papillary thyroid carcinoma recurring as squamous cell carcinoma 10 years after total thyroidectomy: lessons from rapidly progressive papillary thyroid carcinoma.

Primary squamous cell carcinoma (SCC) of the thyroid is very rare. There are no reports of metastatic papillary thyroid carcinoma (PTC) converting to SCC in cervical lymph nodes following total thyroidectomy due to conventional PTC. An 86-year-old woman with a remote history of total thyroidectomy due to PTC underwent palliative neck surgery to treat recurrent bleeding originating from a metastatic tumor of the cervical lymph nodes. The resected mass was composed of mixed SCC and PTC. Although primary SCC rarely occurs in the thyroid, conversion of PTC to SCC should be suspected if preexisting PTC exhibits highly aggressive behavior.