A Case of Metastatic Renal Cell Carcinoma to Thyroid Gland Mimicking as Anaplastic Thyroid Carcinoma

Abstract

Metastatic cancers to the thyroid gland are rare, while the kidney is the most common primary site for metastatic cancers, occupying 42%. Metastatic renal cell carcinoma (RCC) to the thyroid gland usually has no specific symptoms or signs, and no characteristic imaging findings. And metastatic RCC takes a long time to occur after curative treatment. Since RCC rarely metastasizes only to the thyroid gland without the metastasis of other organs, it is difficult to distinguish it from thyroid nodules or cancers with a relatively high prevalence. Unlike metastases from the breast or lung, metastatic RCC to the thyroid gland is difficult to diagnose by a fine needle aspiration biopsy, which is usually confirmed by immunohistochemical analysis after surgery. Therefore, it is difficult to establish a treatment strategy before surgery. Recently, we experienced a rare case of metastatic RCC to the thyroid gland mimicking as anaplastic thyroid carcinoma because of its aggressive clinical course.