Most cancers are named after the part of the body where the cancer first starts. Kidney cancer begins in the kidneys, 2 large, bean-shaped organs. One is just to the left and the other to the right of the backbone. The lower rib cage protects the kidneys.

The kidneys filter the blood and help the body get rid of excess water, salt, and waste products in the form of urine. Urine travels through long tubes (ureters) to the bladder where it is stored until the person passes the urine, or urinates..

Although we have two kidneys, it is possible to survive with less than even 1 complete kidney. Some people live without any working kidneys at all. Their blood is filtered by a machine in a process called dialysis.

The most common type of kidney cancer is called renal cell cancer. It accounts for more than 9 out of 10 cases of kidney cancer. While there are other types of kidney tumors, the information that follows refers only to renal cell cancer. The American Cancer Society has more information about other types of kidney tumors available through our toll-free number or on our Web site.

Like all cancers, kidney cancer begins small and grows larger over time. It usually grows as a single mass within the kidney. But a kidney can have more than one tumor. Sometimes tumors are found in both kidneys at the same time. The cancer might be found only after it has become quite large. Most of the time it is found before it has spread to other organs through the bloodstream.

There are 5 main types of renal cell cancer: clear cell, papillary, chromophobe, collecting duct, and unclassified. Each of these types can be recognized by the way the cells look under a microscope. About 8 out of 10 cases of renal cell cancer are of the clear cell type.

An important feature of kidney cancer is the grade of the cancer. Grade refers to how closely the cancer cells look like normal cells. Kidney cancers are usually graded on a scale of 1 to 4. The lower the number, the more the cancer cells look like normal cells and the better the outlook for the patient. A grade 4 would have cancer cells that look quite different from normal cells and the outlook for the patient would be worse.

While the exact type of cancer cell and the grade of the cancer have some effect on the outlook for survival, the stage (extent of growth and spread) of the cancer is a more important factor. Staging is explained in another section of this article.