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.

In the United States, kidney cancer represents 3% of all cancers, striking 30,000 people annually and killing 12,000 people a year. You risk of kidney cancer is higher if you:

• Smoke cigarettes
• Are obese
• Have had prolonged exposure to asbestos, cadmium or petroleum products (People who work closely with blast-furnaces or "coke-ovens," iron and steel products, dry-cleaning solvents, and gasoline may be at increased risk.)
• Have a family history of kidney cancer
• Have undergone long-term dialysis treatment
• Are between age 50 and 70
• Have tuberous sclerosis, a disease characterized by multiple bumps on the skin caused by small tumors of the blood vessels

Most kidney cancers grow without causing any pain or discomfort. Some kidney cancers are discovered before they begin to cause symptoms. When symptoms develop, renal cell carcinoma can cause an unusually wide variety of symptoms that may not seem obviously related to the kidney. This type of tumor commonly spreads into nearby veins, so it can cause congestion or blockages within the veins. The tumor can also manufacture too much of one or more hormones that are made within the kidney. Symptoms can result from the kidney lump itself, from vein blockage, or from hormonal or chemical effects from the cancer on the body. Some symptoms include:

• Blood in the urine (hematuria)
• Abdominal pain
• An abnormal lump or swelling (mass) in the flank or abdomen
• A constant tired feeling (fatigue)
• Weight loss
• Unexplained fever
• Enlarged lymph nodes
• In men, a collection of enlarged veins in the scrotum (called a varicocele)
• High blood pressure that is not easily controlled
• Breathing difficulty or leg pain caused by blood clots
• Swelling of the abdomen due to accumulated fluid ("ascites")
• Bones that break easily

Since it is common for a person with kidney cancer not to have any symptoms in the early stages, a kidney tumor sometimes is identified by accident when X-rays of the abdomen are taken to evaluate a different health problem. More often, kidney cancer is found after someone has complained of symptoms or during an evaluation to determine why laboratory tests are abnormal.

Abnormal laboratory signs can be the first clue that someone has kidney cancer, and some of them are caused by the cancer's hormone or chemical effects. Abnormal findings might include:

• Anemia (low red blood cell count)
• Elevated red blood cell count (when there is too much of the hormone erythropoietin)
• Abnormal liver function (usually from congestion due to blockage of a vein)
• Abnormal calcium level in the blood
• Abnormal kidney function

During your physical examination, the doctor may be able to feel a mass on one side of your abdomen. If your doctor suspects you have kidney cancer, he or she probably will order a computed tomography (CT) scan of the abdomen and pelvis to look for a tumor. In a CT scan, a modified X-ray beam produces body images at different angles, offering a cross-sectional look at the inside of the kidneys, abdominal organs and pelvic organs.

Other tests that may be used during an evaluation of possible kidney cancer include:

• Intravenous pyelogram  In this X-ray test, a dye is injected into a vein. The dye collects in the kidneys and is excreted in the urine. The dye helps to highlight the path of the urine on an X-ray. This test can help to identify kidney cancer and outline areas of cancer-related kidney damage.
  
   
• Ultrasound  This test uses sound waves to help establish whether a kidney mass is a noncancerous (benign) fluid-filled cyst or a potentially cancerous solid tumor.
  
   
• Chest X-ray  This is used to determine whether kidney cancer has spread to the lungs or to the bones of the chest area.
  
   
• Urinalysis  About 50% of people with renal cell carcinoma have hematuria (blood in the urine). Chemical testing and microscopic examination of the urine can detect small amounts of blood that are not visible to the eye.
  
   
• Magnetic resonance imaging (MRI)  In this test, large magnets and radio waves are used to create cross-sectional, computer-generated pictures of the kidney and nearby organs. This test is especially useful in people who are allergic to the dye used in intravenous pyelography. An MRI also can check to see if cancer has spread to major abdominal blood vessels.
  
   
• Bone scan  In this test, small and safe levels of radioactive materials help to identify where cancer has spread to the bones.
  
   
• Venography  In this X-ray test, a dye is injected into the vein called the inferior vena cava to determine if the cancer has spread into the renal vein and vena cava.
  
   
• Arteriography  In this X-ray test, a dye is injected into an artery leading to the kidney to outline the kidney's blood vessels.
  
   
• Blood tests  A complete blood count (CBC) can show if there are too few red blood cells (anemia) or too many red blood cells (polycythemia), either of which can be seen in people with kidney cancer. Blood chemistry studies also can check for high levels of liver enzymes or calcium, which sometimes accompany kidney cancer.
  
   
• Fine-needle aspiration  In rare cases, a thin sterile needle is used to remove a sample of fluid and cells from the kidney tumor. This sample is examined under a microscope for evidence of cancer.

Most kidney cancers will continue to grow and spread until they are treated. If the cancer can be removed surgically, cure is possible. Non-surgical treatments typically slow the growth of kidney cancer but can not eliminate the tumor.

Your immune system can become very active against tumor cells in kidney cancer, although how much it can control the cancer varies. Except in very rare cases, the immune reaction is not powerful enough to cure the cancer. However, because of the immune system's reaction against the cancer, about 10% of people with metastatic renal cell carcinoma experience a remission, when their cancer stabilizes and does not become worse.

Because 25% to 30% of renal cell carcinoma is linked to cigarette smoking, you may be able to reduce your risk of this cancer by avoiding tobacco. In the workplace, avoid exposure to asbestos and cadmium. To identify early kidney cancer in people receiving dialysis, doctors recommend periodic kidney X-rays.

Treatment is determined by the type of cancer and how far it has spread (its stage), as well as by the person's age, general health and personal preferences. The primary types of treatment for kidney cancers are surgery, biological therapy, chemotherapy and radiation therapy.

Surgery is considered to be the most important treatment for kidney cancer because the chances of surviving without it are poor. However, it is only used to cure kidney cancer when all of the tumor can be removed. Surgery can't cure most people with metastatic disease. However, surgery may have a chance of curing the cancer if it has spread only to nearby tissues. For people whose cancer has spread more widely, surgery can still help, even if it can't cure the cancer. In this case, surgery can remove the most bulky area of tumor, so that a smaller tumor remains for your immune system and medical treatments to fight.

The amount of tissue removed during surgery will depend on the stage and type of kidney cancer. Among the surgical procedures available are the following:

• Radical nephrectomy  The entire kidney, adrenal gland and surrounding lymph nodes and fatty tissue are removed. For some cancers, nephrectomy can be done using the camera-guided surgery known as laparoscopy, which uses smaller incisions than traditional surgery.
  
   
• Partial nephrectomy  Only the portion of the kidney that contains cancer cells is removed. There is a risk that a small amount of cancer may be left behind.
  
   
• Arterial embolization  A small tube (catheter) is inserted into an artery in the groin and moved through the blood vessel until it reaches the kidney's artery. Then material is injected into the artery to block it. This technique can be used before a nephrectomy to stop any kidney bleeding and to kill some of the cancer cells.
  
   
• Metastases removal  When kidney cancer has spread to distant sites, these sites are called metastases. Surgically removing metastases can provide temporary relief from pain and other symptoms in the immediate area, but it does not help the person to survive longer.

Biological therapy, also called immunotherapy, is the most common treatment for advanced kidney cancer. It helps the body's immune defenses fight and destroy cancer cells. There are three types of biological therapy:

• Proteins that activate the immune system (cytokines), such as interleukin-2 and interferon-alpha
• A tumor vaccine that promotes the production of cytokines within cancer cells
• Transplantation of cells from another individual (bone marrow transplant or white blood cell infusion) to enhance the attack of immune cells on the cancer.

Both the tumor vaccine for renal cell carcinoma and transplantation procedures for this disease are still experimental, but they are being offered to an increasing number of people due to their success in early studies.

A variation on biological therapy for renal cell carcinoma treatment is antibody therapy or other treatments that are directed specifically against new growth of blood vessels. These agents are called angiogenesis inhibitors. These treatments may help to slow the growth of renal cell carcinoma, but they are currently considered experimental treatments.

Radiation therapy relies on high-energy radiation to kill cancer cells. This therapy can be used along with other treatments to minimize symptoms.

Traditional chemotherapy (anticancer drugs) are taken by mouth or delivered through a vein into the bloodstream. These medicines are not as effective as biological therapies against renal cell carcinoma. Traditional chemotherapy is effective for kidney cancer caused by transitional cell carcinoma and renal sarcoma. Chemotherapy drugs commonly used to treat transitional cell carcinoma of the kidney include methotrexate (Rheumatrex, Trexall), vinblastine (Velban, VLB), doxorubicin (Adriamycin, Rubex, Doxil) and cisplatin (Platinol-AQ). Medicines useful for treating renal sarcoma include carboplatin (Paraplatin), cisplatin (Platinol-AQ), paclitaxel (Taxol, Onxol), gemcitabine (Gemzar) and doxorubicin (Adriamycin, Rubex, Doxil). All have side effects, such as nausea, fatigue, vomiting and hair loss.