Renal cell carcinoma (RCC) has a high metastatic potential, and most commonly metastasizes via the bloodstream, although lymphatic metastases also occur. RCC is well-known for its propensity to metastasize to unusual sites, and late metastasis, even after a number of years, is common. The occurrence of RCC metastasis to the head and neck region is uncommon, and occurs primarily in the thyroid gland and in patients with widespread dissemination. Involvement of the parathyroid gland in metastatic carcinoma is extremely rare. In the present report, a case of metastasis confined to the parathyroid gland is described, likely with intrathyroidal localization, arising from a RCC that occurred 16 years after nephrectomy. A 66-year-old man was referred to the Department of Surgery of the University Hospital of Pisa (Pisa, Italy) with a preoperative fine-needle aspiration diagnosis of a follicular lesion in the context of nodular goiter of the thyroid gland. The previous medical history of the patient included a right nephrectomy for the treatment of clear cell RCC in February 1997. No other distant metastases were identified as of the latest follow-up in March 2014. At the time of thyroid surgery, the thyroid and parathyroid function tests were normal. The gross appearance of the surgical specimen was a multinodular goiter with a solid nodule measuring 33 mm on the left lobe of the thyroid gland. Microscopic examination revealed a completely encapsulated lesion consisting of clear cells arranged in a solid pattern and intermixed with fragments of parathyroid tissue. Following immunohistochemical examination, the clear cell lesion was negative for thyroid transcription factor-1 and thyroglobulin and strongly positive for epithelial membrane antigen, cluster of differentiation 10 and vimentin. To the best of our knowledge, this is the second case of metastasis to the parathyroid gland from a RCC reported in the literature.
Keywords: clear cell; immunohistochemistry; metastasis; parathyroid; renal carcinoma.