More Than Meets the Eye: a Case of Synchronous Ipsilateral Clear Cell Renal Cell Carcinoma and Urothelial Carcinoma of the Pelvicalyceal System

Abstract Background: The synchronous occurrence of renal cell carcinoma and urothelial carcinoma of the renal pelvis in the same kidney is extremely rare, although previously reported. To our knowledge, we present the youngest patient recorded in the literature, with this histology combination presenting synchronously in the same kidney, and the first report in active duty military personnel.Case presentation: An otherwise healthy 43-year-old military male with the chief complaint of left plank pain was seen in the office. Imaging revealed the presence of a 3.5 cm left renal mass. Left laparoscopic radical nephrectomy was performed for presumed renal malignancy. Pathology confirmed the presence of a clear cell RCC and revealed an area of low-grade UC arising from the ipsilateral renal pelvis, not visible in the preoperative imaging. Conclusions: Although uncommon, the final pathology report may reveal neoplasms of dissimilar histology that may involve the renal pelvis. It is crucial for urologists and pathologists to be vigilant of such cases during a solid renal mass workup. Additional therapeutic adjustments may be necessitated, derailing the initial treatment plan. Novel biomarkers of cancer stem-like cells may play a role in the management of these patients.