Renal cell carcinoma metastasis to thyroid tumor: a case report and review of the literature

INTRODUCTION Metastatic neoplasms to the thyroid gland are rare in clinical practice. Clear cell renal carcinoma is the most frequent site of origin of thyroid metastases and represents 12 to 34% of all secondary thyroid tumors. Tumor-to-tumor metastases, in which a thyroid neoplasm is the recipient of a metastasis, are exceedingly rare. We report a case of clear cell renal carcinoma metastatic to a follicular adenoma. This is the tenth case of renal cell carcinoma metastasis to thyroid tumor reported in the literature. CASE PRESENTATION A 62-year-old Caucasian woman with a history of clear cell renal carcinoma was admitted to our institution for multinodular goiter. A histological examination after total thyroidectomy revealed clear cell renal carcinoma metastasis to a thyroid follicular adenoma. CONCLUSIONS Preoperative diagnosis of secondary thyroid neoplasm is difficult to achieve. The diagnosis of metastatic disease should be taken into account if patients have a history of clear cell renal carcinoma or if there is a multifocal growth pattern and clear cell appearance of the cytoplasm.