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case_images: Abdominal enhanced computed tomography scans demonstrating the right posterior peritoneal tumor lesion. (A) at diagnosis in February 2020; (B) at disease relapse 4.5 months after RNU; (C) the tumor lesion was enlarged following 2 weeks of first dose of tislelizumab treatment in July 2020; (D) liquefaction and cystic changes were observed within the tumor lesion following 6 weeks of tislelizumab combined with anlotinib treatment in August 2020; (E-G) continuous shrinkage of the tumor lesion following tislelizumab combined with anlotinib treatment in October 2020, January 2021, and May 2021, respectively; (H) disease progression following 20 months of tislelizumab combined with anlotinib treatment in February 2022.
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case_images: The abdominal enhanced computed tomography (CT) showed a 3.5 cm x 2.5 cm right renal pelvic upper mass lesion with uneven enhancement ( Figure 1A ). Abdominal enhanced CT revealed renal pelvic carcinoma recurrence and invasion of the posterior peritoneum and inferior vena cava ( Figure 1B ). Two weeks later, the reexamination CT revealed a significant increase in the primary lesion's tumor size ( Figure 1C ). By the sixth week, CT scan showed significant liquefaction and cystic changes within the tumor lesion ( Figure 1D ), the patient reported continuous relief of clinical symptoms, indicating a response to ICI/TKI (tislelizumab plus anlotinib) combination therapy. The multiple abdomen enhanced CT examinations showed a continuous shrinkage of the right posterior peritoneal tumor lesion, and the clinical response evaluation was PR ( Figures 1E-G ). In this follow-up, CT scan revealed an enlargement of the right posterior peritoneal lesion which was diagnosed as progressive disease (PD) ( Figure 1H ).
case_images: Histopathologic diagnosis: urothelial carcinoma of the right renal pelvic with sarcomatoid carcinoma differentiation. Conventional invasive high-grade urothelial carcinoma components (arrows) and sarcomatoid components (dotted circle).
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case_images: The postoperative pathological diagnosis was infiltrating UC with sarcomatoid carcinoma differentiation ( Figure 2 ).
case_images: Treatment timeline.
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case_images: The treatment flowchart is shown in  Figure 3 .