Anaplastic transformation of thyroid cancer: Report of two cases and review of the literature

Transformation of well-differentiated thyroid adenocarcinoma to anaplastic cancer has been occasionally reported. Two new cases of such transformation are now described. The time interval from diagnosis to the development of anaplastic cancer was 15 years in the first patient and 10 years in the second. Both patients ultimately developed extensive bilateral pulmonary metastases and died within 6 months from the diagnosis of the transformation. Hypotheses concerning the pathogenesis of the transformation and the literature were reviewed. We believe that histopathological confirmation of recurrent and rapidly progressive thyroid tumors is necessary prior to initiation of therapy.