The majority of upper tract uroepithelial tumors are of transitional cell histology. Squamous cell cancer of the urinary tract constitutes less than 15% of the tumors of the renal pelvis and a smaller percentage of ureteral tumors and is often associated with chronic calculus disease and infection.

Grade of transitional cell cancer of the upper tract has generally been found to correlate with stage. Superficial tumors are generally grade I or II, whereas the majority of infiltrative tumors are grades III and IV. Prognosis is worse for patients with high-grade (grades III and IV) tumors than for those with low-grade (grades I and II) tumors.