Clear cell renal cell carcinoma (CCRCC) is the most common origin for
metastasis in the thyroid. A 51-year-old woman was referred to our hospital for a subcarinal lesion. Ten years before, the patient had undergone a
nephrectomy for CCRCC. Whole-body fluorodeoxyglucose positron emission tomography revealed elevated values in the thyroid gland, while the mediastinum was normal. An endoscopic ultrasonography-guided fine-needle aspiration biopsy of the mediastinal mass was consistent with CCRCC, and this was confirmed after resection. The
thyroidectomy specimen also revealed
lymphocytic thyroiditis, nodular
hyperplasia, one
follicular adenoma, two papillary microcarcinomas, and six foci of metastatic CCRCC involving both thyroid lobes. Curiously two of the six metastatic foci were located inside two adenomatoid nodules (
tumor-in-
tumor). The metastatic cells were positive for cytokeratins, CD10,
epidermal growth factor receptor, and
vascular endothelial growth factor receptor 2. No BRAF gene mutations were found in any of the primary and metastatic lesions. The patient was treated with
sunitinib and finally died due to CCRCC distant
metastases 6 years after the
thyroidectomy. In CCRCC patients, a particularly prolonged survival rate may be achieved with the appropriate
therapy, in contrast to the ominous prognosis typically found in patients with thyroid
metastases from other origins.