Squamous Cell Carcinoma Metastatic to the Thyroid Gland Diagnosed by Fine-Needle Aspiration Cytology: A Case Report.

Fine-needle aspiration cytology of the thyroid gland has been widely used for the initial diagnosis of suspected malignant thyroid nodules and definitive preoperative diagnosis of recurrent and metastatic thyroid cancer. Metastases to the thyroid most commonly arise from tumors in the lungs, kidneys, breasts, and skin. Metastatic squamous cell carcinoma can also be observed in the thyroid, but it is relatively rare. Here, we report a case of esophageal squamous cell carcinoma metastatic to the thyroid that was diagnosed using fine-needle aspiration cytology, relying on cytomorphological characteristics, immunohistochemical features, and other clinical clues.