Kidney Cancer

What Is It?

The kidneys are two bean-shaped, fist-sized, organs below the rib cage in the back, to the right and left of the spine. They serve as the body's filters to clean the blood of waste products, excess water and salt. They also produce a hormone called renin, which monitors blood pressure, and a hormone called erythropoietin, which regulates the production of red blood cells.

Kidney cancer is an uncontrolled growth of abnormal kidney cells that invade and destroy the normal kidney tissue and can spread (metastasize) to other organs. There are three major types of kidney cancer in adults:

• Renal cell carcinoma - Renal cell carcinoma begins in the lining of the small tubes that mass together to make up the kidney. It accounts for 85% of all kidney cancers. Although renal cell carcinoma typically develops as a single tumor in only one kidney, it sometimes involves both kidneys. Most of these tumors are discovered before any tumor has spread through the bloodstream or lymph system to other organs. There are three different types of renal cell carcinoma: clear cell tumors (75% of all renal cell carcinomas), granular cell tumors and sarcomatoid tumors. These types are identified according to how they look under the microscope and the specific type of abnormality in their genetic code.

• Transitional cell carcinoma - Transitional cell carcinoma begins in draining kidney tubes as they exit the kidney. It represents 6% to 7% of all kidney cancers. This cancer looks different under the microscope than renal cell carcinoma, and it usually begins in the renal pelvis (the funnel-shaped area that connects the ureter to the main portion of the kidney). Studies suggest that transitional cell carcinoma is linked to cigarette smoking.

• Renal sarcoma - Renal sarcoma begins in blood vessels within the kidney or from a mutation of a more common cancer type. It is the rarest form of kidney cancer, and accounts for only 1% of cases.

When children develop kidney cancer, it is usually a cancer of kidney cells from early development. This childhood tumor is called nephroblastoma, and it is commonly known as Wilms' tumor.