EBV negative lymphoepithelioma-like carcinoma of the thyroid gland: a rare entity and incidental presentation

Abstract

Abstract Background: Lymphoepithelioma-like carcinoma (LELC) is a rare entity among thyroid tumors. Primary LELC of the thyroid was previously named as intrathyroidal epithelial thymoma and carcinoma showing thymus-like differentiation (CASTLE) and the association with EBV has been inconsistently detected. This paper presents fine-needle aspiration cytology (FNAC) findings along with histologic features of LELC in a middle-aged female patient with incidental metastatic disease. Case presentation: A previously healthy 29-Year-old female who had an incidental palpable nodule in the right thyroid lobe on routine annual checkup. Thyroid U/S showed a 1.5 cm hypoechoic solid nodule with ill-defined margins. FNAC revealed papillary architecture and a few psammoma bodies on the background of dense lymphocytic infiltration. Thyroseq genomic sequencing revealed gene expression alterations with no gene mutation. The patient went for total thyroidectomy and right lymph node level 4 resection. The histologic slides of the nodule revealed solid arborizing bands of oval to spindled cells, associated with lymphoplasmacytic infiltrate and scattered psammoma bodies on the background of lymphocytic thyroiditis. There were no classic patterns of papillary or any aggressive features. Immunohistochemically, the tumor was positive for TTF1, PAX-8, and P40. In situ hybridization for EBV-encoded RNA was negative in the tumor cells. The patient has no tumor recurrence on 6-month follow up. Conclusion: Because LELC is very rare in the thyroid gland, careful clinical examination along with IHC stainings specific for thyroid follicular cells can help in proving its thyroid origin. Additionally, we hope to raise the awareness for this peculiar variant for accurate clinicopathological diagnosis.