Loss of cellular polarity/cohesiveness and periostin expression are involved in the epithelial-mesenchymal transition in the epithelial malignancies. Their roles in papillary thyroid carcinoma were studied. There was a significant correlation between the loss of cellular polarity/cohesiveness in the invasive front and the up-regulation of periostin in tumors. Both of them were significantly correlated with extrathyroid invasion, pT and lymph node metastasis. Our results suggest that the loss of cellular polarity/cohesiveness is a useful parameter for predicting prognosis of patients with papillary thyroid carcinoma, and periostin could be a candidate gene for therapeutic targeting for the blockage of tumor invasion.