E-cadherin loss rather than beta-catenin alterations is a common feature of poorly differentiated thyroid carcinomas.

To investigate the immunohistochemical and molecular genetic features of the cadherins/catenins complex in thyroid carcinoma based on the hypothesis that poorly differentiated carcinoma of the thyroid represents an intermediate step between well-differentiated and undifferentiated carcinomas. Immunohistochemistry for E-, P- and N-cadherins and alpha-, beta- and gamma-catenins was performed in a series of 17 cases of poorly differentiated carcinoma of the thyroid. All cases showed absence of membranous expression of E-cadherin with no aberrant expression of P- or N-cadherins; regarding catenins there was heterogeneous loss of expression with membranous immunolocalization of the three catenins in most cases. Molecular analysis of the E-cadherin gene and exon 3 of the beta-catenin gene was also performed by polymerase chain reaction/single-strand conformation polymorphism and sequencing. No mutations in either gene were detected in any case. In contrast to previous reports, our results suggest that loss of E-cadherin rather than beta-catenin mutation is the crucial event in determining the differentiation 'level' of thyroid carcinomas.