Our research on urothelial carcinoma of the upper urinary tract (UTUC) mainly focusses on the bladder recurrences following surgery for this disease. As 22-47% of the surgical treated UTUC patients will develop such a recurrence this is an important issue in clinical practice for UTUC. With the REBACARE-trial we hope to make a significant change to the current guidelines, with a much saver preoperative instillation with MMC prior to a radical nephroureterectomy, instead of following surgery to lower the risk on bladder recurrences. As little is known about the molecular aspects of UTUC we also focus on the genetics and genomics of UTUC within MOLCARUTUC-collaboration (Erlangen, Paris, Malaga, Rotterdam), a European funded study for rare cancers. Within this study we also hope to unravel the question if these bladder recurrences are indeed clonally related to the primary UTUC.