Metastatic Clear Cell Renal Cell Carcinoma Masquerading as Urinary Bladder Tumor: A Report of a Rare Case.

Clear cell renal cell carcinoma (ccRCC) is known to be the most common histological subtype of renal cell carcinoma, with a well-known potential for distant metastasis. Common metastatic sites are the lungs, liver, bones, and brain; however, metastasis to the urinary bladder is exceptionally rare. We describe a 64-year-old man with a history of high-grade ccRCC who developed painless gross hematuria six months after undergoing right radical nephrectomy. Cystoscopic evaluation revealed two polypoidal bladder masses. Histopathological and immunohistochemical analyses confirmed metastatic ccRCC (positive for carbonic anhydrase IX (CAIX), paired-box gene 8 (PAX8), and cluster of differentiation 10 (CD10)). The patient was managed by transurethral resection of bladder tumor (TURBT) followed by targeted therapy with sunitinib (37.5 mg). He remains disease-free at one-year follow-up. This case underscores the importance of considering metastatic recurrence in patients with a prior history of RCC who present with new-onset urinary tract symptoms. Although rare, bladder metastasis should be included in the differential diagnosis. The underlying mechanism remains speculative, with possible routes including hematogenous spread, retrograde venous dissemination, or direct seeding. ccRCC can metastasize to unusual sites, including the urinary bladder. Early recognition through comprehensive imaging and immunohistochemical evaluation is essential for timely diagnosis and management.