In this prospective translational multicenter study, clinical data, peripheral blood and sequential tumor biopsies are collected from urothelial cancer patients treated with second-line treatment with pembrolizumab to identify the role of immune evasive mechanisms combined with genomic characterization. A pre-treatment tumor biopsy and blood sample will be obtained and subsequently whole genome sequencing and whole genome RNA sequencing is performed. Both tumor tissue as well as peripheral blood will be investigated for immune and molecular profiling. A biopsy will also be taken after start of treatment (at 6 weeks) and at progression (optional)