Challenges in diagnosing and managing sarcomatoid urothelial carcinoma of the renal pelvis: a case report - Lei, Jian; Zhao, Wei; He, Tao; Huang, Hui; Jian, Huayong; Zhang, Mei; Luo, Xike; Gong, Xiaochuan; Wang, Yan (Frontiers in Oncology, 2025)