Cytokeratin 5/6 and P63 immunophenotype of thyroid lymphoepithelial complexes

Thyroid lymphoepithelial complexes (LECos) are rare, being reported in lymphoma, Graves-Basedow disease, Hashimoto thyroiditis, pericarcinomatous thyroid or in the context of branchial cleft-like cysts. Here we report immunohistochemical expression of cytokeratin 5/6, P63 and TTF1 in 6 cases of thyroid LECos. Two cases had carbimazole treatment for hyperthyroidia and Graves disease. Anti-thyroglobulin, -thyroperoxidase or -TSH antibodies were detected in 4 cases. NSAID or poviodone iodine allergy were present in 2 cases. The treatment consisted in total thyroidectomy or lobectomy. Microscopy showed nodular goiter and focal lymphocytic thyroiditis. Basaloid LECos were seen in all thyroids while squamoid LECos in 2. Associated lesions were papillary thyroid microcarcinoma (2 cases), solid cell nest, thyroglosal duct remnant, lymphoepithelial cyst and thymus-parathyroid unit (one case each). Cytokeratin 5/6 was expressed in both squamoid and basaloid LECos along with P63. TTF1 expression was faint or absent. In conclusion LECos may occur in the context of autoimmune thyroiditis or of a specific immune susceptibility background. The expression of CK5/6 and of P63 suggests a squamous differentiation including in the basaloid LECos. The etiologic relevance of these immunostainings remains limited although rather suggestive of a metaplastic process than of migration-abnormalities.