Papillary carcinoma occurring within an adenomatous goiter of the thyroid gland in Cowden's disease

Cowden's disease is an autosomal dominant disorder characterized by multiple benign and malignant neoplastic lesions involving many organs. The presence of characteristic cutaneous lesions is crucial for the diagnosis. Thyroid disease is a major extracutaneous manifestation of this disease; however, the histologic characteristics have not been described in detail. We report a case of thyroid tumor associated with Cowden's disease. Grossly, the tumor showed a multinodular appearance, like an adenomatous goiter. Microscopically, it consisted of follicular adenomas with a trabecular pattern. Some of the nodules had a second component resembling papillary carcinoma. This was thought to be a unique histological feature not described previously, and might be specific to thyroid tumor associated with Cowden's disease.