The goal of this observational study is to evaluate the intravesical recurrence (IVR) rate after ureteroscopy (diagnostic or treatment) for upper tract urothelial carcinoma (UTUC) followed by an adjuvant single instillation of Mitomycin C (SI-MMC). The main question it aims to answer are: * What is the total and time to IVR after 2 years after ureteroscopy (diagnostic or treatment) for UTUC * How is the IVR compared with a historical cohort (no SI-MMC) * What is the time to IVR after 2 years in patients who subsequently received treatment by endoscopy vs. radical nephroureterectomy (RNU) * What is the additional value of a SI-MMC on time to IVR after RNU + adjuvant MMC in patients who were evaluated by ureteroscopy prior to RNU