Abstract
INTRODUCTION: The Multiple primary malignant tumors (MPMT) refers to the occurrence of two primary malignant tumors in the same organ or organs in the same patient at the same time. However, MPMT is rare in the urinary system. Congenital urinary tract anomalies (e.g., duplex systems) predispose patients to recurrent infections, stones, and rare malignancies, creating diagnostic and therapeutic challenges. CASE PRESENTATION: The patient was an elderly woman presenting with left low back pain and fever. Initial evaluation revealed left duplex kidney with ureteral malformation, complicated by upper kidney abscess, left kidney stone, and ureteropelvic junction stone. A ureteral stent was placed for symptom relief. After admission, enhanced CT/MRI identified left renal rupture with stone leakage, upper renal tumor, and ureteral tumor. Histopathology confirmed high-grade renal cell carcinoma (RCC) and urothelial carcinoma in situ (CIS), classified as a rare "duplication carcinoma." Diagnostic delays occurred due to severe tumor necrosis masking imaging features, inconclusive initial endoscopy, and overlapping symptoms of systemic infection. The patient's complex anatomy (duplex kidney) and multifocal pathology (tumors, stones, infection) required multidisciplinary reevaluation to differentiate malignancy from inflammatory processes. CLINICAL DISCUSSION: This case is a high-grade renal cell carcinoma with urothelial carcinoma in situ, which meets the definition of repeat carcinoma. The pathogenesis of this case may be due to the development of malformations of the kidney and ureter combined with tumor compression of the collecting system, which will lead to long-term inadequate drainage and secondary stones, infection, etc. Early diagnosis is the key to improve the survival rate of patients with synchronous carcinomas. Enhanced CT combined with magnetic resonance imaging can be used for initial diagnosis. CONCLUSIONS: Synchronous carcinomas (synchronous RCC and urothelial CIS) in a duplex kidney with stones/pyonephrosis is exceptionally rare, emphasizing the need for vigilance in congenital anomalies. Complex cases demand tailored strategies, integrating urologic, oncologic, and radiologic expertise to address anatomical anomalies, infection, and malignancy simultaneously. Early suspicion of neoplasia in refractory cases is critical to avoid delays.