Investigation of the clonal origin of multifocal papillary thyroid carcinoma according to the X-chromosome inactivation pattern

Patients with papillary thyroid carcinoma (PTC) usually have multiple tumors, or foci. It remains unclear if these foci originate from independent tumors or a single tumor mass. The present study included 89 female patients with bilateral PTC who had been treated with a total thyroidectomy. An X-chromosome inactivation assay was used to examine the clonal origin of the tumors according to the status of the X-linked human androgen receptor gene. Of the 89 patients, 5 were informative. The X-chromosome inactivation pattern was the same in multiple foci in 3 cases, indicating a monoclonal origin of the tumors. In 1 case, the X chromosome inactivation pattern was different between the tumors. Mixed patterns were observed in 1 case. The results of the present study suggest that in certain cases of multifocal PTC, tumors arise independently, whereas in other cases, separate foci are the outcome of intra-thyroid spread by a single tumor mass.