Kidney cancer is also called renal carcinoma. It is a cancer that starts in the kidneys. In order to understand kidney cancer, it helps to know how the normal kidneys look and work.

About the kidneys

The kidneys are about the size of your fist. These 2 bean-shaped organs are shown in the picture below. One is just to the left and the other to the right of the spine. The lower rib cage protects the kidneys.

The kidneys' main job is to filter your blood and help the body get rid of excess water, salt, and waste products. The waste is made into urine. Urine travels through long, thin tubes (called ureters) to the bladder where it is stored until you urinate.

We have 2 kidneys, but a person can live with less than even one complete kidney. Some people live without any working kidneys at all. Their blood is filtered by a machine in a process called dialysis.

Renal cell carcinoma

The most common type of kidney cancer is called renal cell cancer (also known as RCC, renal cell carcinoma, or renal cell adenocarcinoma). It accounts for more than 9 out of 10 cases of kidney cancer. While there are other types of kidney tumors, the information here refers only to renal cell cancer.

Like all cancers, kidney cancer begins small and grows larger over time. It usually grows as a single mass or tumor within the kidney. But a kidney can have more than one tumor. Sometimes tumors are found in both kidneys at the same time. Kidney tumors are often found on CT scans or ultrasounds being done for concerns other than kidney cancer. The cancer might be found only after it has become very large. Most of the time it is found before it has spread to other organs. This is good because like most cancers, kidney cancer can be hard to treat after it has spread (metastasized).

Types of kidney cancer

There are several subtypes of renal cell cancer (RCC), based mainly on how the cancer cells look under a microscope:

Clear cell renal cell carcinoma: This is the most common form of RCC. About 8 out of 10 people with RCC have this kind of cancer. When seen under a microscope, the cells that make up clear cell RCC look very pale or clear.

Papillary renal cell carcinoma: This is the second most common subtype -- about 10% to 15% of people with RCC have this kind. These cancers make little finger-like projections (called papillae) in some, if not most, of the tumor. Some doctors call these cancers chromophilic because the cells take up certain dyes used to prepare the tissue to be looked at under the microscope. The dyes make them look pink.

Chromophobe renal cell carcinoma: This subtype accounts for about 5% of RCCs. The cells of these cancers are also pale, like the clear cells, but are much larger and differ in other ways, too.

Collecting duct renal cell carcinoma: This subtype is very rare. The major feature is that the cancer cells can form irregular tubes.

Unclassified renal cell carcinoma: In rare cases, renal cell cancers are labeled as "unclassified" because they don't fit into any of the other groups or because more than one type of cell is present.

Other kidney tumors that are cancer

Transitional cell carcinoma: About 5% to 10% of cancers in the kidney are transitional cell carcinomas, also known as urothelial carcinomas. Transitional cell carcinomas begin where the kidney meets the ureter. Under the microscope, the cells look like bladder cancer cells. People with transitional cell carcinoma often have the same signs and symptoms as people with renal cell cancer -- blood in the urine and, sometimes, back pain.

These cancers are usually treated by removing the whole kidney and the ureter, as well as the part of the bladder where the ureter attaches. Smaller cancers can sometimes be treated with less involved surgeries. Chemotherapy is sometimes given after surgery. It's important to talk with your doctor so you know your options and the benefits and risks of each treatment. About 9 out of 10 transitional cell carcinomas of the kidney can be cured if they are found at an early stage.

Wilms tumor: About 5% of all kidney cancers are Wilms tumors. This type of cancer is almost always found in children and is very rare in adults. If you want to learn more about this type of cancer, call 1-800-ACS-2345 and ask for the ACS document, Wilms Tumor.

Renal sarcoma: Renal sarcomas are a rare type of kidney cancer that begins in the kidney's connective tissue. Renal sarcomas are discussed in more detail in the ACS document, Sarcoma -- Adult Soft Tissue Cancer.

Last Medical Review: 04/02/2009
Last Revised: 05/06/2009