The purpose of this observational study is to assess the role of plasma concentration monitoring of treatment drugs for patients with metastatic renal cell carcinoma (mRCC) in terms of efficacy and side effects. It furthermore holds microbiome characterization of CPI-treated patients. Furthermore, the investigators examines the role of anti-drug antibodies and receptor polymorphisms in CTLA-4 and PD-1 receptors in treatment failure among patients with mRCC treated with check point immunotherapy (CPI). Moreover, polymorphisms in the UGT1A1 gene will be correlated with the pazopanib treatment dose.