Solitary Metachronous Metastasis to the Thyroid from Renal Clear Cell Carcinoma 19 Years After Nephrectomy: Report of a Case

We report a rare case of a solitary metachronous metastasis of renal clear cell carcinoma (RCC) presenting as a thyroid tumor 19 years after a nephrectomy. Our search of the English-language literature found only sporadic reports of late RCC metastases to the thyroid. Fine-needle aspiration biopsy of the thyroid tumor was not accompanied with thyroglobulin (Tg) staining, leading us to initially suspect a primary follicular thyroid carcinoma. The patient, a 77-year-old man, underwent a total thyroidectomy with modified neck dissection. Histological examination confirmed the tumor to be RCC metastasis, and immunohistochemical analysis revealed that both Tg and thyroid transcription factor-1 (TTF-1) were negative in the tumor cells. Thus, the possibility of late RCC metastasis to the thyroid should be considered, even in a patient with a remote history. Furthermore, TTF-1 is useful for identifying thyroid metastatic carcinomas.