Clear cell urothelial carcinoma: a rare but villainous and hostile subtype.

Clear Cell Urothelial Carcinoma (CCUC) is a rarely reported urothelial carcinoma variant first described in 1995. Due to CCUC's clinical rarity, reporting additional cases may aid future clinicians on surgical and oncological management. We present a case of an 89-year-old male with primary CCUC and highlight the aberrant histopathological findings with a literature review. This study aims to add to current descriptions of CCUC and inform surgical and oncological management in future patients. An 89-year-old male with a history of smoking presented to clinic with painless hematuria of six months duration. Imaging showed right-sided hydroureteronephrosis down to a bladder mass. This was confirmed to be a bladder tumor on office cystourethroscopy. Following TURBT procedure, the pathology report came back suggesting 3.6 cm superficial low-grade Ta CCUC. Five months later, the patient presented with hematuria, acute kidney injury, and anemia. He was found to have T3a muscle-invasive urothelial carcinoma. This was confirmed on additional analysis which showed an FGFR3 mutation and abundant glycogen-filled clear cells. Histologically, CCUC is characterized by a glycogen-rich clear cytoplasm, severe atypia and a "nested" growth pattern. CCUC may be differentiated from non-CCUC by as few as a 30% clear cell change morphology of all cells. CCUC must be differentiated from Renal Cell Carcinoma and Clear Cell Adenocarcinoma. Treatment for CCUC has varied by case, with some surgeons electing to treat with radical cystectomy while others opting for local resection. Our case helps combat the paucity of literature by further characterizing and contributing to the management of CCUC.