A case of a man with biphasic sarcomatoid carcinoma of the right kidney wit
h chondrosarcomatous foci and with invasion of the pelvic mucosa and submuc
osa into the peripelvic adipose tissue is presented. In situ carcinoma of t
he urothelium of the right renal pelvis and proximal ureter was also noted.
Comments on the nomenclature of malignant tumours with apparently mixed ca
rcinomatous and sarcomatous phenotypes and a hypothesis on the histogenesis
of these tumours are presented. Cytokeratin and p53 protein expression pat
terns, and the results of angiogenesis quantification are consistent with a
n epithelial-to-mesenchymal conversion induced by the stroma.