Scott Tagawa, MD, MS, Weill Cornell Medicine, New York, NY, outlines the clinical implications of hyperphosphatemia seen in advanced urotherlial carcinoma patients treated with erdafitinib and how clinicians may be able to use this in vivo biomarker in assessing the treatment of their patients. This interview took place at the European Society for Medical Oncology (ESMO) 2019 congress in Barcelona, Spain.