Squamous cell carcinoma of the renal pelvis with sarcomalike stroma: a light and electron microscopic study with immunohistochemical analysis.

Primary neoplasms of the renal pelvis are rare. Most are malignant, and most of these are transitional cell carcinomas. We report the unusual occurrence of a squamous cell carcinoma with sarcomatoid stroma arising from the renal pelvic mucosa in a patient with renal lithiasis. Immunohistochemical stains for keratin intermediate filaments failed to demonstrate their presence in the spindle cell portion of the tumor. Transmission electron microscopic study did not reveal structures of an epithelial nature in these same cells. Our findings support the contention that the spindle cells of the stroma are not squamous in nature, but represent either a reactive or a neoplastic transformation of these underlying stromal elements.