What is kidney cancer?
Kidney cancer is also called renal carcinoma. In order to understand kidney cancer, it helps to know how the normal kidneys look and work.
About the kidneys
The kidneys are a pair of bean-shaped organs, each about the size of a fist. They are shown in the picture below. One is on either side of the spine. The lower ribcage 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 (pee).
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. Like most cancers, RCC is hard to treat once it has spread.
Types of kidney cancer
There are several subtypes of renal cell cancer (RCC), based mainly on how the cancer cells look under a microscope. Knowing an RCC subtype can be a factor in choosing treatment and can also help your doctor figure out if your cancer may be due to an inherited genetic syndrome.
Clear cell renal cell carcinoma: This is the most common form of RCC. About 7 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 1 out of 10 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 a few cases of RCCs. The cells of these cancers are also pale, like the clear cells, but are much larger and differ in other ways.
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 don’t start in the kidney itself but rather in the lining of the renal pelvis (where the urine goes before it enters the ureter). This lining is made up of cells called transitional cells that look like the cells that line the bladder under the microscope. The cells of this kind of cancer 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.
To find out more about transitional cell carcinoma, see our document, Bladder Cancer.
Wilms tumor: About 5% of all kidney cancers are Wilms tumors or nephroblastomas. This type of cancer is almost always found in children and is very rare in adults. If you want to learn more, see our document, Wilms Tumor.
Renal sarcoma: Renal sarcomas are a rare type of kidney cancer that starts in the kidney’s connective tissue or blood vessels. Renal sarcomas are discussed in more detail in our document, Sarcoma-Adult Soft Tissue Cancer.
The rest of this document is about renal cell carcinoma and not other types of kidney tumors.
Last Medical Review: 11/27/2012
Last Revised: 01/23/2013