About the kidneys
The kidneys are a pair of reddish-brown bean-shaped organs, each about the size of a small fist, that are located above the waist on either side of the spine. They are closer to the back of the body than to the front. Kidneys filter blood and remove impurities, excess minerals and salts, and extra water. Every day, the kidneys filter about 200 quarts of blood to generate two quarts of wastewater (urine).
The kidneys also produce hormones to help control blood pressure, red blood cell production, and other functions. Although most people have two kidneys, each works independently, which means that the body can function with less than one complete kidney. With dialysis, a mechanized filtering process, it is possible to live without kidneys.
Types of kidney cancer
Kidney cancer begins when normal cells in one or both kidneys change and grow uncontrollably, forming a mass called a tumor. A tumor can be benign (noncancerous) or malignant (cancerous, meaning it can spread to other parts of the body).
There are several types of kidney cancer:
Renal cell carcinoma. Renal cell carcinoma makes up about 85% of kidney cancer. This cancer develops within the kidney's microscopic filtering systems, the lining of tiny tubes that lead to the bladder.
Transitional cell carcinoma. This is also called urothelial carcinoma. Transitional cell carcinoma begins in the area of the kidney where urine collects before moving to the bladder. This type of kidney cancer is similar to bladder cancer and is treated like bladder cancer . It accounts for 10% to 15% of kidney cancer in adults.
Sarcoma. Sarcoma  of the kidney is rare and is treated with surgery. For some patients, it may be beneficial to combine chemotherapy with surgery, as sarcoma can grow quite large before it is discovered. It does not metastasize (spread) as often as other types of kidney cancer.
Wilms tumor. Wilms tumor  is most common in children and is treated differently than kidney cancer in adults. This type of tumor is more likely to be successfully treated with radiation therapy and chemotherapy than the other types of kidney cancer, and this has resulted in a different approach to treatment.
Types of kidney cancer cells
Knowing which kind of cell a tumor is made of helps doctors plan treatment. There are several types of kidney cancer cells. The most common are listed below. Pathologists (doctors who specialize in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease) have identified as many as 10 different types of these cells.
- Clear cell is the type of cell that is found in about 70% of kidney cancer. Clear cells range from slow growing (grade 1) up to fast growing (grade 4). This type of kidney cancer is particularly responsive to immunotherapy and targeted therapy (see Treatment ).
- Papillary kidney cancer, which develops in 10% to 15% of patients, is divided into two different subtypes, called type 1 and type 2. They are different from the clear cell type, although papillary kidney cancer is currently treated the same as clear cell kidney cancer. However, many doctors may recommend treatment in clinical trials  because treatment with targeted therapy is often not as successful for papillary kidney cancer as with clear cell kidney cancer.
- Sarcomatoid is the type of cell that grows the fastest. It may be found with clear cell or papillary type. It is called sarcomatoid because it looks like sarcoma under a microscope.
- Collecting duct is a rare cancer that behaves similar to transitional cell carcinoma. It is best treated with chemotherapy. However, many doctors believe that it is less responsive to chemotherapy than transitional cell carcinoma but more responsive than clear cell or sarcomatoid types.
- Chromophobe is another rare cancer that is different from other types.
- Oncocytoma is a slow-growing type that rarely, if ever, spreads.
- Angiomyolipoma is a benign tumor that has a unique appearance on the computed tomography (CT or CAT) scan (see Diagnosis ) and when viewed with a microscope; it tends to be less likely to grow and spread and is best treated with surgery.
Find out more about basic cancer terms used in this section .
Looking for More of an Overview?
If you would like additional introductory information, explore these related items on Cancer.Net:
- ASCO Answers  Fact Sheet: Read a one-page fact sheet (available in PDF) that offers an easy-to-print introduction for this type of cancer.
- Cancer.Net En Español: Read about kidney cancer in Spanish . Infórmase sobre el cáncer de riñón en español. 
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