Pazopanib: the newest tyrosine kinase inhibitor for the treatment of advanced or metastatic renal cell carcinoma

Abstract

Treatment options for renal cell carcinoma (RCC) have multiplied in the past 5 years. Pazopanib is the third tyrosine kinase inhibitor (TKI) and the sixth targeted therapy that has received US FDA approval for the treatment of advanced or metastatic RCC. The primary mechanism of action of pazopanib in RCC is through its antiangiogenic properties via inhibition of the intracellular tyrosine kinase of vascular endothelial growth factor receptor and platelet-derived growth factor receptor. A placebo-controlled phase III study demonstrated that pazopanib significantly improved response rates and progression-free survival (PFS) in both treatment-naïve and cytokine-pretreated patients. Among treatment-naïve patients, the response rate was 32% and PFS was 11.1 months. In cytokine-pretreated patients, the response rate and PFS were 29% and 7.4 months, respectively. Common adverse effects of pazopanib include diarrhoea, hypertension and elevation of liver enzymes. Overall, the adverse effect profile of pazopanib is similar to that of other TKIs used for the treatment of RCC, but variation in the incidence and severity may exist. Pazopanib has an increased propensity to cause hepatotoxicity, which may be fatal in rare cases. Hepatic function must be monitored closely with dose interruption and/or reduction if elevation of hepatic function tests occurs. Pazopanib is administered on an empty stomach at a dose of 800 mg daily until disease progression, but dose reduction may be required in patients with baseline elevation of hepatic function tests, particularly total bilirubin. The minimum dose recommended for baseline hepatic dysfunction or toxicity is 200 mg daily. The potential for drug interactions exists for pazopanib. It is a substrate of cytochrome P450 (CYP) 3A4, P-glycoprotein and breast cancer resistance protein, and it weakly inhibits CYP3A4, CYP2C8 and CYP2D6, and potently inhibits UGT1A1 and OATP1B1. Currently, no study has directly compared pazopanib with other first- or second-line therapies in RCC. However, published clinical trials of pazopanib show similar efficacy outcomes to those of other targeted therapies. Therefore, pazopanib may be considered a first-line treatment option among other therapies including sunitinib, temsirolimus, and bevacizumab plus interferon-α. After failure of cytokine therapy, pazopanib is a treatment option as well as sorafenib or bevacizumab. No study has evaluated pazopanib treatment after failure of another targeted therapy. Future studies will further clarify the comparative efficacy of pazopanib with other agents as well as optimal sequencing with other agents. If similar efficacy is seen among the TKIs, it is likely that varying incidences of adverse effects may be analysed to tailor therapy according to the patient's individual co-morbidities and preferences.