Increasing evidences have demonstrated the roles of epithelial-mesenchymal transition in tumor invasion and metastasis. In the invasive front of papillary thyroid carcinoma, the expressions of adhesion molecules are often lost. In anaplastic thyroid carcinoma, tumor cells showing cancer stem cell characteristics have been identified. Epithelial-mesenchymal transition may thus play a key role in the progression of thyroid cancer. Therefore, it provide new insight for the development of targeted drugs for anaplastic thyroid carcinoma.