Alpha-catenin Mutation-associated Synchronous Follicular Thyroid Carcinoma and Papillary Thyroid Carcinoma With Numerous Adenomatoid Nodules

Background/Aim: The relationship between germline catenin alpha 1 (CTNNA1) mutation and thyroid neoplasia remains poorly understood. We report a case with a pathogenic germline CTNNA1 mutation and an unusual constellation of thyroid proliferative lesions. Case Report: A 59-year-old woman with a history of invasive ductal carcinoma of the breast was incidentally found to have a thyroid nodule on chest computed tomography (CT). Fine-needle aspiration and repeat biopsies demonstrated multiple follicular-patterned lesions, prompting thyroid lobectomy. Histopathologic examination revealed synchronous minimally invasive follicular thyroid carcinoma (FTC) (2.3 cm) and classic papillary thyroid carcinoma (PTC) (2.5 mm) arising in a background of innumerable adenomatoid nodules diffusely involving thyroid parenchyma. Immunohistochemical studies demonstrated diffuse CK19 positivity with decreased E-cadherin and increased cyclin D1 and p53 expressions in the PTC. Genetic testing identified a pathogenic heterozygous CTNNA1 mutation without evidence of phosphatase and tensin homolog (PTEN) alteration. Conclusion: This case expands the spectrum of germline CTNNA1-associated disease and raises the possibility that diffuse multifocal thyroid proliferative lesions with thyroid carcinomas may represent an underrecognized manifestation of CTNNA1-related hereditary cancer predisposition.