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

Background: 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.

Methods: 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.