Case of pazopanib-induced thyrotoxicosis in a patient with metastatic renal cell carcinoma.

Pazopanib is an oral multi-targeted tyrosine kinase inhibitor and has been approved for metastatic renal cell carcinoma and advanced soft tissue sarcoma. To the best of our knowledge, pazopanib-induced thyrotoxicosis has never been reported. The patient was a 68-year-old woman with renal cell carcinoma and multiple metastases. Three weeks after pazopanib medication, she felt fatigue and palpitation. She was admitted because of liver chemistry abnormalities [AST 723 IU/L (normal range 7-37 IU/L); ALT 953 IU/L (normal range 3-33 IU/L)]. She showed abnormal thyroid function tests with suppressed TSH of 0.0585 μIU/mL, and elevated fT4 of 3.38 ng/dL. Ten days after admission, tachycardia appeared and fT3 and fT4 were elevated (fT3 27.85 pg/mL, fT4 2.58 ng/dL), and TSH was suppressed (0.0414 μIU/mL). Her thyroid ultrasound showed hypervascular thyroid gland without nodules. We diagnosed pazopanib-induced thyrotoxicosis. Because the fT3/fT4 ratio was high (10.8) and the thyroid was enlarged, we thought that her thyrotoxicosis might get worse. She was treated with medication of beta-blockers, hydrocortisone, and potassium iodide and thyrotoxicosis resolved. This report highlights that Pazopanib could induce thyrotoxicosis, and therefore, periodic surveillance of thyroid function is required during pazopanib therapy.