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 12-34% of all secondary thyroid tumours. Tumour-to-tumour 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 10th case of renal cell carcinoma metastasis to thyroid tumour reported in literature. Case presentation. A 62-year-old Caucasian woman with history of CCRC was admitted to our institution for multinodular goiter. Histological examination after total thyroidectomy revealed CCRC metastasis to a thyroid follicular adenoma. Conclusion. 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 CCRC or if there is a multifocal growth pattern and clear cell appearance of the cytoplasm.