Nuclear localization of immunoreactive beta-catenin is specific to familial adenomatous polyposis in papillary thyroid carcinoma

Thyroid carcinoma is the first symptom in some patients with familial adeno matous polyposis (FAP). We evaluated the cellular localization of beta -cat enin in thyroid carcinomas associated (n=4) or not associated (n=173) with FAP, since loss of functional protein of the adenomatous polyposis coli (AP C) gene leads to nuclear accumulation of beta -catenin in adenomas and carc inomas of the FAP colon. Immunoreactive beta -catenin was demonstrated at t he cell membrane of glandular cells of the non-neoplastic thyroid and non-F AP carcinomas. On the other hand, cytoplasmic and nuclear accumulation of b eta -catenin is specific to FAP-associated papillary carcinomas. The abnorm ality in the APC/beta -catenin pathway is thus also important in FAP-associ ated thyroid carcinoma, and beta -catenin immunohistochemistry is a feasibl e screening method to identify occult FAP in young patients with thyroid tu mors.