E-cadherin: a differentiation marker in thyroid malignancies.

Loss of E-cadherin (uvomorulin), a Ca(2+)-dependent cell adhesion molecule required for normal epithelial function, has been attributed a pathogenetic role in tumor invasion. The expression of E-cadherin was studied in normal and neoplastic follicular epithelium of the human thyroid by Northern blot analysis and immunofluorescence on frozen tissue sections. In the normal thyroid (n = 10) and in benign thyroid disorders (n = 21; toxic diffuse goitre; multinodular goitre; follicular adenomas), E-cadherin mRNA levels were equally high and the follicles were generally stained, mainly along the lateral surface of the epithelial cells, by the anti-E-cadherin monoclonal antibody. In anaplastic thyroid carcinomas (n = 6) E-cadherin expression was very low or lacking. In papillary carcinomas (n = 23), E-cadherin mRNA levels varied from nearly normal to highly reduced, which roughly correlated with the overall immunofluorescence intensity. However, the immunostaining also revealed a heterogeneous "all-or-nothing" expression of E-cadherin among adjacent cells in the same tumor. In the follicular carcinomas (n = 9), E-cadherin mRNA levels were in general rather high but the immunostaining varied considerably. A few papillary and follicular tumors lacked immunoreactive E-cadherin in spite of high mRNA levels. In oxyphilic (Hürthle) cell tumors, comprising both adenomas (n = 4) and carcinomas (n = 2), E-cadherin immunoreactivity was reduced and distributed intracellularly rather than at the cell surface. The expression of E-cadherin in relapsing thyroid carcinomas and in tumors with metastatic spreading was, irrespective of the histiotype, low or lacking. Sequential Northern analysis revealed a close correlation between the expression levels of E-cadherin and the thyrotropin receptor. Together, the data suggest that in human thyroid malignancies both gene expression and posttranscriptional control of E-cadherin may be impaired.