Abstract
Metastasis of renal cell carcinoma to the thyroid gland is rare. We report two cases of metastatic renal carcinoma to the thyroid gland. The first case was that of a 68-year-old male patient who had undergone right nephrectomy for renal cell carcinoma 12 years earlier. He was referred to us for an enlarging mass in the right lobe of the thyroid gland. Fine needle aspiration cytology revealed suspected papillary carcinoma with intranuclear cytoplasmic inclusions. Therefore, right hemithyroidectomy was performed. Metastatic renal carcinoma was diagnosed because the histopathological findings were suggestive of a clear cell carcinoma. The second case was that of a 52-year-old female patient who had undergone left nephrectomy for renal cell carcinoma 6 years earlier. She was referred to our department because a follow-up CT scan had revealed a thyroid mass. Fine needle biopsy cytology of the thyroid mass showed a follicular lesion, therefore, the patient was observed for a while. However, as the thyroid mass had enlarged, isthmus excision was performed. The patient was diagnosed as having metastatic renal carcinoma because the histopathological findings were suggestive of a clear cell carcinoma. Since kidney cancers may cause distant metastasis after long periods of time, thyroid mass with a past history of renal cell carcinoma should be considered as a metastatic renal cell carcinoma. As for the treatment, excision of the metastatic lesion is the treatment of first choice. Since excision of a distant metastasis has been reported to prolong the survival in patients with renal cell carcinoma, aggressive excision is desirable in the case of distant metastasis to the head and neck region.
