(KID-nee KAN-ser) Cancer that forms in tissues of the kidneys. The most common type of kidney cancer in adults is renal cell carcinoma. It forms in the lining of very small tubes in the kidney that filter the blood and remove waste products. Transitional cell cancer of the renal pelvis is kidney cancer that forms in the center of the kidney where urine collects. Wilms tumor is a type of kidney cancer that usually develops in children under the age of 5.