EndocrineThe relationship between the follicular variant of papillary thyroid cancer and follicular adenomas

BackgroundReports suggest that the incidence of tumors diagnosed as follicular variant of papillary thyroid cancer (FVPTC) is increasing and that this increase may reflect changes in diagnostic criteria with tumors presently being diagnosed as FVPTC previously being defined as follicular lesions, in particular follicular adenomas. Changes during recent years in the relationship between the incidence of FVPTC and follicular adenomas have not been reported. Herein, we have compared changes in the incidence of FVPTC with changes in the incidence of follicular adenomas.MethodsThe study is a retrospective analysis of a prospective database of patients undergoing thyroid surgery between January 1, 2004, and December 31, 2013.ResultsA total of 953 thyroid procedures performed in 851 patients were reviewed. The incidence of FVPTC increased approximately 4-fold during the study period when expressed as percentage of all thyroidectomies with the increase mainly reflecting an increase in the incidence of noninvasive FVPTC. The incidence of follicular adenomas decreased in a reverse fashion resulting in a >10-fold increase in the ratio between FVPTC and follicular adenomas during the study period.ConclusionAlthough the present results suggest that some tumors previously diagnosed as follicular adenomas are increasingly classified as FVPTC, in particular noninvasive FVPTC, the possibility that the results at least in part also reflect a true increase in the incidence of FVPTC cannot be ruled out. If the increased incidence of FVPTC reflects a lowered threshold for the diagnosis of FVPTC it is possible that some tumors presently being classified as FVPTC are overdiagnosed as cancer and may currently be treated more aggressively than needed.