Absence of mutations in the beta-catenin and adenomatous polyposis coli genes in papillary and follicular thyroid carcinomas.

beta-Catenin has multiple functions both in intercellular adhesion and in signal transduction. As a signaling molecule, mutations in exon 3 of the beta-catenin gene stabilize this protein in the cytoplasm. Subsequently, accumulated beta-catenin protein translocates to nuclei with T-cell factor-4, and upregulates transcriptional activity of the target genes involved in carcinogenesis. Mutations in exon 3 of the beta-catenin gene have been detected in various carcinomas. We examined immunolocalization of beta-catenin protein and mutations in the beta-catenin and adenomatous polyposis coli (APC) genes in papillary carcinoma (25 cases), follicular carcinoma (two cases), and benign thyroid tumor (29 cases). We detected no mutation in exon 3 of the beta-catenin gene in both malignant and benign thyroid tumors by polymerase chain reaction (PCR) and direct sequencing. No mutations in the mutation cluster region of APC were found in any tumor samples analyzed. Immunohistochemically, beta-catenin showed membranous localization in most specimens. These results suggest that mutations of the beta-catenin and APC genes are rare and that activation of the Wnt signaling pathway may not contribute to pathogenesis in human papillary and follicular thyroid carcinomas.