Most studies report that TCV accounts for 5% to 10% of papillary carcinomas, although the percentage of TCV in the tumor
required for a diagnosis has not been entirely consistent. In addition, the TCV must be differentiated from the similar columnar cell variant characterized by similar “tall cells” that have stratified rather than basal nuclei. The reported cooccurrence of TCV and columnar cell variants suggests a similar pathogenesis for both tumors. TCV has also been associated with anaplastic carcinomas in a manner similar to that of insular carcinoma. In addition, a high incidence of mutations in the p53 tumor-suppressor gene has been reported in TCV, further supporting its “transitional” nature.

Patients with TCV, like those with other dedifferentiated tumors, tend to be older and present with larger tumors. They are also more likely to present with local invasion or metastases.23 The typical female predominance of thyroid cancer is seen for TCV.

Patients with TCV tend to present in a similar manner to those with well-differentiated papillary cancer, albeit at a later age. The frequency of local metastases is relatively high, and distant metastases are more common than for papillary carcinoma (19%).23,29,30 and 31,31a Occasionally, young individuals with small intrathyroidal TCV cancers are identified. Much controversy exists regarding the natural history of these tumors.