Results: Ber-EP4 expression was detected in normal thyroid tissue (perilessional), in all the adenomas, follicular carcinomas, and medullary carcinomas. Papillary carcinomas showed in 36 % lacking areas of expression, coinciding histopathologically one case with poorly differentiated component. All of the poorly differentiated and the anaplastic carcinomas were negative. Conclusion: The expression of Ep-CAM, using Ber-EP4, was related to normal thyroid tissue and well differentiated neoplasms. Our study suggest that lost of expression is associated to dedifferentiation. This results match up with the literature. In addition, clinical data and follow up are required to correlate focal areas of lost of expression of Ber-EP4 with dedifferentiated areas of the tumor.