Renal cell carcinoma metastasis to the thyroid gland after drug-induced thyroid dysfunction: case report.

Objective: Renal cell carcinoma may be associated with highly aggressive behavior and metastatic disease may be present in 30% of patients at the time of diagnosis. The most common sites of metastasis are the lungs, regional lymph nodes, liver, and bones. Metastases at rare sites include gums, larynx, nasal cavity, and thyroid gland. The objective of this article is to report an unusual manifestation of a known disease and present emerging technology useful in patient management. Clinical case: A 60-year-old male patient with a history of renal cell carcinoma. He initially received onco-specific treatment with nephrectomy and, ten years later, with zoledronate, pazopanib, and nivolumab due to metastatic progression. Four months after starting systemic treatment, drug-induced thyroid dysfunction was diagnosed, manifested by fatigue and abnormal laboratory results (TSH 9,23 uUI/mL). Due to the sensation of a lump in the neck, an ultrasound revealed a thyroid nodule on the right side. Aided by doppler ultrasound, and strain elastography, an ultrasound guided fine-needle aspiration biopsy of the thyroid nodule was performed, which confirmed metastasis of renal cell carcinoma. Conclusion: The emergence of a thyroid nodule in patients with a history of renal cell carcinoma and thyroid dysfunction could indicate oncological progression, even a long time after the initial diagnosis.