Like other major organs in your body, your kidneys can sometimes develop cancer. In adults, the most common type of kidney cancer is renal cell carcinoma (renal adenocarcinoma or hypernephroma), which begins in the cells that line small tubes (tubules) within your kidneys. Children are more likely to develop a kind of kidney cancer called Wilms' tumor.

• back pain
• 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. Cancer cells may also spread (metastasize) outside your kidneys to nearby organs such as your adrenal glands, pancreas and spine, as well as to more distant sites in your body. Yet if kidney cancer is detected and treated early, the chances for a full recovery are good.

Signs and symptoms

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 it may be detected by urinalysis, a test that specifically checks the contents of your urine.

• Urinalysis

Other possible signs and symptoms may include:

• A pain in your back just below your ribs that doesn't go away

• A mass in the area of your kidneys that's discovered during an examination

• Weight loss

• Fatigue

• Intermittent fever

• Pain in other parts of your body if the cancer has metastasized

Wilms' tumor usually has no symptoms. Doctors often discover this condition when examining a child's abdomen.

• fatigue

• fever

• Wilms' tumor

Causes

Your kidneys are part of a complex system (urinary system) that removes waste and excess fluid 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 known as nephrons. As blood circulates through your kidneys, the nephrons filter out waste products as well as unneeded minerals and water. This liquid waste — urine — drains through two narrow tubes (ureters) into your bladder, where it's stored until it's eliminated from your body though another tube, the urethra.

Renal cell carcinoma, which accounts for almost 90 percent of all 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 you may develop tumors in both kidneys.

A far less common type of kidney cancer, transitional cell carcinoma, may occur inside the kidneys, ureters or bladder, and 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.

• sarcoma

Risk factors

The risk of renal cell carcinoma increases as you age. This type of kidney cancer occurs most often in people between the ages of 50 and 70. 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 are nonsmokers. The risk increases the longer you smoke and decreases after you quit.

• Obesity. A strong link exists between excess weight and renal cell carcinoma in both men and women. Weighing more than is healthy for you may cause changes in certain hormones — changes that in turn may lead to cancer.

• High blood pressure (hypertension). Researchers have found a link between high blood pressure and renal cell carcinoma. Although it appears that your risk decreases when you're treated for high blood pressure, it's also possible that diuretic medications used to treat hypertension may play a role in this type of 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 (VHL) disease. People with this inherited disorder develop benign blood vessel tumors (hemangioblastomas) in their brain and spinal cord and may develop tumors of the adrenal glands. They're also at high risk of kidney cancer.

• Hereditary papillary renal cell carcinoma. Having this inherited condition makes it more likely you'll develop one or more renal cell carcinomas.

• high blood pressure

• lung cancer

• Nicotine dependence

• Obesity

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 at increased risk of developing transitional cell carcinoma of the ureter or kidney as well as developing additional bladder cancers. By the same token, having transitional cell kidney cancer makes it more likely you'll develop bladder cancer.

• Phenacetin. Long-term use of this painkiller has led to kidney cancer in some people.

• Bladder cancer

• Glomerulonephritis

• Nicotine dependence

When to seek medical advice

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 your kidneys' filtering function. In rare cases, you may even notice blood in your urine after strenuous exercise such as a marathon run.

• Glomerulonephritis

• Urinary tract infection - (UTI)

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.

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