Your kidneys are two bean-shaped organs, each about the size of your fist. They're located behind your abdomen, one on each side of your spine. Like other major organs in the body, the kidneys can sometimes develop cancer. In adults, the most common type of kidney cancer is renal cell carcinoma (renal adenocarcinoma), which begins in the cells that line the small tubes within your kidneys. Children are more likely to develop a kind of kidney cancer called Wilms' tumor.

Kidney cancer seldom causes problems in its early stages. But as a tumor grows, you may notice blood in your urine or experience unintentional weight loss or back pain that doesn't go away. Kidney cancer cells may also spread (metastasize) outside your kidneys to nearby organs as well as to more distant sites in the body. Yet if kidney cancer is detected and treated early, the chances for a full recovery are good.

Kidney cancer rarely causes signs or symptoms in its early stages. In the later stages, the most common sign of both renal cell and transitional cell cancers is blood in the urine (hematuria). You may notice the blood when you urinate, or your doctor may detect it by urinalysis, a test that specifically checks the contents of your urine. Other possible signs and symptoms may include:

• A pain in the back just below the ribs that doesn't go away
• A mass in the area of the kidneys that's discovered during an examination
• Weight loss
• Fatigue
• Intermittent fever
• Pain in other parts of the body if the cancer has metastasized

Wilms' tumor usually has no symptoms, and doctors are likely to discover this condition when examining a child's abdomen.

Your kidneys are part of the urinary system, which removes waste and excess fluid and electrolytes from your blood, controls the production of red blood cells, and regulates your blood pressure. Inside each kidney are more than a million small filtering units called nephrons. As blood circulates through your kidneys, the nephrons filter out waste products as well as unneeded minerals and water. This liquid waste — urine — flows through two narrow tubes (ureters) into your bladder, where it's stored until it's eliminated from your body through another tube, the urethra.

Renal cell carcinoma, which accounts for most kidney cancers, usually begins in the cells that line the small tubes (tubules) that make up a part of each nephron. In most cases, renal cell tumors grow as a single mass, but you may have more than one tumor in a kidney or develop tumors in both kidneys.

A far less common type of kidney cancer, transitional cell carcinoma, develops in the tissue that forms the tubes connecting the kidneys to the bladder. Transitional cell carcinomas can also begin in the ureters themselves or in the bladder. A rare form of kidney cancer, renal sarcoma, begins in the connective tissue of the kidney.

Just what causes kidney cells to become cancerous isn't clear. But researchers have identified certain factors that appear to increase the risk of developing both renal and transitional cell kidney cancers.

The risk of renal cell carcinoma increases with age; most kidney cancers occur in people 60 and older. Men are more than twice as likely as are women to develop renal cell carcinoma, and black men have a slightly higher risk than white men do. Other risk factors for renal cell carcinoma include:

• Smoking. Smokers, especially those who smoke pipes or cigars, are at greater risk than nonsmokers are. The risk increases the longer you smoke and decreases after you quit, although it takes years to reach the same risk level as someone who has never smoked.
• Obesity. A strong link between excess weight and renal cell carcinoma exists in both men and women. In fact, obesity may account for as many as one-third of renal cell carcinomas.
• High blood pressure (hypertension). Having high blood pressure makes it more likely you'll develop renal cell carcinoma, and the risk increases further if you're also overweight. Although treating high blood pressure appears to reduce this risk, diuretic medications used to treat hypertension actually may contribute to kidney cancer.
• Environmental toxins. Coal oven workers in steel plants have high rates of kidney cancer. So do people who are exposed to cadmium, to organic solvents such as trichloroethylene and to asbestos, a fireproofing material that has also been linked to lung cancer.
• Dialysis. People who receive long-term dialysis to treat chronic renal failure are at greater risk of developing kidney cancer, possibly because renal failure depresses the immune system. People who have a kidney transplant and receive immunosuppressant drugs also are more likely to develop kidney cancer.
• Radiation. In some cases, exposure to radiation may increase your risk of kidney cancer.
• Von Hippel-Lindau disease. People with this inherited disorder are likely to develop several kinds of tumors, including, in some cases, renal cell carcinoma.
• Hereditary papillary renal cell carcinoma. Having this inherited condition makes it more likely you'll develop one or more renal cell carcinomas, but unlike people with Von Hippel-Lindau disease, you're not at unusually high risk of other types of tumors.

Risk factors for transitional cell carcinoma include:

• Cigarette smoking. This is the leading risk factor for transitional cell carcinomas. A history of smoking can quadruple your risk of this type of cancer.
• Exposure to industrial chemicals. These include heavy metals, asbestos and aniline dyes.
• Bladder cancer. People who have bladder cancer are more likely to develop transitional cell carcinoma of the ureter or kidney as well as additional bladder cancers. And having transitional cell kidney cancer makes it more likely you'll develop bladder cancer.
• Phenacetin. Although no longer available in the United States, the analgesic medication phenacetin has been known to cause kidney cancer in some people.

See your doctor right away if you notice blood in your urine. In most cases, this doesn't mean you have kidney cancer. Blood in the urine may be a sign of many conditions, including a renal cyst — a noncancerous lesion of the kidney that's common in people older than 50 — bladder or kidney stones, prostate problems, urinary tract infections or glomerulonephritis, a kidney disease that affects the kidneys' filtering function. In rare cases, you may even notice blood in your urine after strenuous exercise such as a marathon run.

If you think you may be at risk of developing kidney cancer, discuss your concerns with your doctor. He or she may suggest ways to reduce your risk and can schedule regular checkups. When kidney cancer is diagnosed early, it's easier to treat and your chances of survival are good. Once cancer has spread, however, treatment is more difficult and the prognosis is less positive.

In addition to taking a complete medical history and performing a physical exam, your doctor will likely recommend blood and urine tests. If your doctor suspects a problem or if you are at high risk of kidney cancer, you may also have one or more of the following tests to check for growths or tumors:

• Intravenous pyelogram (IVP). In this test, a contrast dye is injected into a vein in your arm. A series of X-rays is taken as the dye moves through your kidneys, ureters and bladder.
• Ultrasound examination. An ultrasound isn't an X-ray. Instead, it uses high-frequency sound waves to generate images of your internal organs, such as your kidneys and bladder, on a computer screen.
• Computerized tomography (CT) or magnetic resonance imaging (MRI) scan. CT scans use computers to create more detailed images than those produced by conventional X-rays. MRI scans use magnetic fields and radio waves to generate cross-sectional pictures of your body.
• Biopsy. In this test, a sample of tissue is removed and examined under a microscope. It's the only way to confirm the presence of cancer. Biopsies are commonly performed on tumors that develop in a ureter or in the kidney pelvis — the area at the center of the kidneys where urine collects. A solid kidney tumor, on the other hand, is often removed without a biopsy because these tumors are almost always cancerous and because a needle biopsy may spread cancer cells outside the biopsied kidney.

Tests for transitional cell cancer
If the results of an IVP suggest transitional cell cancer, your doctor will likely recommend a test that examines your bladder for signs of cancer (cystoscopy). In this procedure, a long, narrow tube called a cystoscope is inserted through your urethra into your bladder. The tube carries a light source and special lens, which allow your doctor to inspect both your urethra and bladder. The cystoscope can also be used to remove a small tissue sample from a tumor. In some cases, a microscopic examination of the sediment in your urine may also help identify cancer cells.

Tests to determine whether cancer has spread
If your doctor finds signs of kidney cancer, the next step is to determine whether the cancer has spread. This usually means more tests, including additional blood tests, an ultrasound of your liver, a CT scan, a chest X-ray or a bone scan. A bone scan is a test in which you're given a small amount of a radioactive material that's then taken up by your bones. Tumors absorb even more of this material and show up as a black area when a special camera scans your body.

Second opinions
If you've received a diagnosis of kidney cancer, you may want to seek a second opinion. Sometimes your insurance company may even require you to do so. In that case, your current doctor may be able to recommend other specialists. In addition, the Cancer Information Service at (800) 4-CANCER, or (800) 422-6237, can provide information on treatment centers. You can also get a list of doctors from your local hospital or a nearby medical school.

Together, you and your treatment team — which may include a surgeon, a doctor who specializes in disorders of the urinary organs (urologist), a cancer specialist (oncologist) and an oncologist who specializes in treating cancer with radiation (radiation oncologist) — will discuss all of your options. The best approach for you may depend on a number of factors, including your general health, the kind of kidney cancer you have and whether the cancer has spread.

Renal cell carcinoma
Treatments for renal cell carcinoma include:

• Surgical removal. Until recently, the standard treatment for cancer that was confined to the kidney was surgical removal of the entire kidney (radical or simple nephrectomy). In a radical nephrectomy, surgeons remove the kidney along with the adrenal gland that sits atop the kidney, a border of normal tissue and adjacent lymph nodes. A simple nephrectomy involves removing the entire kidney, although not the adrenal gland or lymph nodes. But studies show that removing just the tumor (nephron-sparing surgery), rather than the whole kidney, results in survival rates similar to those of more radical procedures. In addition, people who have nephron-sparing surgery appear less likely to develop chronic kidney failure and are more likely to enjoy a better quality of life than do those who have the whole kidney removed.

  Sometimes surgeons may choose to remove the entire kidney because of the extent and the location of the tumor. In that case, laparoscopic nephrectomy may offer advantages over traditional open surgery because it typically results in less postoperative pain, faster recovery time and less scarring. In a laparoscopic procedure, a tiny camera is inserted into your body through a small incision. The camera transmits video images that allow your surgeon to see the kidney in great detail. The surgeon inserts surgical instruments through two or three additional small incisions and performs the operation. The recovery time and side effects of any type of kidney surgery will vary, but it's likely you'll feel tired and weak for a time, even with laparoscopic nephrectomy.

• Arterial embolization. In this procedure, a radiologist injects a special material into the main blood vessel leading to the kidney. By clogging this vessel, the tumor is deprived of oxygen and other nutrients. Arterial embolization may be used before an operation or to relieve pain and bleeding when an operation isn't possible. Side effects may include temporary nausea, vomiting or pain.
• Radiation therapy. This therapy uses radiation to kill cancer cells. It's usually used to relieve pain when kidney cancer has spread to the bones. In general, you'll receive radiation treatment at a clinic or hospital on an outpatient basis — often five days a week for several weeks. The effects of radiation are cumulative, and you may become very tired in the last few weeks of treatment. The skin in the treated area may become red, tender or itchy, and you also have other side effects, such as nausea and vomiting.
• Immunotherapy. This treatment uses your body's immune system to fight cancer. An oncologist may administer a substance known as a biological response modifier, such as interferon or interleukin-2. Normally produced by the body, these substances are also made in laboratories. Studies show that people may do better when they're treated with both interferon and surgery, rather than with interferon alone. Biological response modifiers can have serious side effects, including chills, fever, nausea, vomiting and loss of appetite. You may bruise easily after treatment and feel extremely tired. Interleukin-2 and interferon therapies can also affect liver and kidney function. These side effects are often severe, but usually disappear once treatment is stopped.
• Chemotherapy. This therapy, which uses drugs to attack rapidly dividing cells, hasn't proved particularly useful for renal cell carcinoma.

Transitional cell cancer
To treat transitional cell cancer in its early stages, surgeons remove an area surrounding the tumor while trying to save the kidney itself. If the tumor is too large or too centrally located, the kidney and ureter may need to be removed along with the portion of the bladder that's connected to the ureter. This helps decrease the risk of cancer cells spreading to the bladder. Chemotherapy is often used to treat transitional cell cancer that has spread.

Wilms' tumor
Treatment for children with Wilms' tumor depends on the child's age and overall health, the type of tumor and whether the cancer has spread. In many cases, treatment may include surgical removal of the tumor followed by chemotherapy or radiation.

Clinical trials
If kidney cancer has spread, standard treatments are seldom effective. For that reason, you may choose to participate in a clinical trial. These trials test the effectiveness and side effects of new treatments. Those who take part have a chance to receive a treatment that may be promising but not yet widely available. If you're interested in clinical trials, talk to your doctor. You can also contact the National Cancer Institute for detailed information, or visit the clinical trials page on its Web site.

Although the following steps may not prevent kidney cancer, they can help reduce your cancer risk and keep you healthier overall:

• Quit smoking. Smokers are nearly twice as likely to develop kidney cancer as nonsmokers are. Talk to your doctor about the best ways to stop smoking.
• Eat more fruits and vegetables. In the past, some studies have shown that a diet rich in fruits and vegetables may help protect against kidney cancer. A 2005 Swedish study looked at which types of produce might offer the most benefits. The study found an overall association between consumption of fruits and vegetables and a lower risk of kidney cancer. Further, the study found the strongest association was for study participants eating bananas and root vegetables, including beets and carrots.
• Stay physically active. An active lifestyle reduces your risk of kidney cancer and helps you lower your blood pressure and maintain a healthy weight. Aim for at least 30 minutes of exercise on most days. If you haven't been active before, start out slowly, and gradually increase the amount of time you exercise. Try to include weight-bearing exercises, such as walking, jogging or dancing as well as some strength-training exercises in your routine. Strength training has been found to reduce stress even more than aerobic exercise does, and it has the added benefit of helping keep your bones strong.
• Maintain a healthy weight. There is a clear link between weighing more than is healthy for you and kidney cancer.
• Reduce or avoid exposure to environmental toxins. If you must work with toxic chemicals, take special precautions such as wearing a mask and heavy gloves.
• Reduce high blood pressure. If you have, or think you may have, high blood pressure — which has been linked to renal cell carcinoma in men — talk to your doctor. Diet and exercise can control high blood pressure in many cases.

Eating well, managing stress and exercising are ways to promote your overall health and cope with any form of cancer.

Eating well
Good nutrition is especially important for people undergoing cancer treatment. But eating well can be difficult, especially if your treatment includes chemotherapy or radiation treatment. You may feel nauseated or lose your appetite, and foods may seem tasteless. You may find that the last thing you want to do is plan meals.

Even so, eating well during cancer treatment can help you maintain your stamina and your ability to cope with the side effects of treatments. Good nutrition may also help you prevent infections and remain more active.

Remember these strategies for eating well when you don't feel well:

• Eat protein-rich foods. Foods high in protein can help build and repair body tissues. Choices include eggs, yogurt, cottage cheese, peanut butter, poultry and fish. Kidney beans, chickpeas and black-eyed peas also are good sources of protein, especially when combined with rice, corn or bread.
• Keep an open mind about the foods you might eat. Foods that are unappealing today might taste better to you next week.
• When you do feel well, make the most of it. Eat as many healthy foods as you can. Prepare meals that you can easily freeze and reheat. Also look for low-fat frozen dinners and other prepared foods.
• Give meals a pleasant atmosphere. Whenever possible, eat at a table set with attractive dishes and flowers.
• Pack calories into the foods you eat. For example, spread butter, jam or honey on bread. Sprinkle foods with chopped nuts.
• Eat smaller amounts of food more frequently. If you can't face the thought of a large meal, try eating small amounts of food more often. Keep fruits and vegetables handy for snacking.

Managing stress
Methods for reducing physical tension can help you manage stress. One simple and powerful technique is to simply close your eyes and notice your breathing. Pay attention to each inhalation and exhalation. Your breathing will become slower and deeper, promoting relaxation. Another technique is to lie down, close your eyes and mentally scan your entire body for any points of tension.

Exercise
In addition, activities that require repetitive movements, such as running and swimming, can produce a mental state similar to meditation. So can yoga and other stretching exercises.

Your doctor may have more specific suggestions about how to best care for yourself before, during and after treatment for kidney cancer.