An infiltrating transitional cell carcinoma that arises from the renal pelvis and exhibits sarcomatoid features. The disease is kidney pelvis sarcomatoid transitional cell carcinoma (Monarch Disease Ontology identifier MONDO_0004009). Also known as: infiltrating renal pelvis urothelial carcinoma, sarcomatoid variant, renal pelvis sarcomatoid transitional cell carcinoma, sarcomatoid transitional cell carcinoma of kidney pelvis, sarcomatoid transitional cell carcinoma of renal pelvis, sarcomatoid transitional cell carcinoma of the kidney pelvis, sarcomatoid transitional cell carcinoma of the renal pelvis.