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Kidney cancer accounts for about 2 to 3% of cancers in adults, affecting about 50% more men than women. Smokers are about twice as likely to develop kidney cancer as nonsmokers. Other risk factors include exposure to toxic chemicals and obesity. People affected are usually between 50 and 70 years of age.
Most solid kidney tumors are cancerous, but fluid-filled tumors (cysts) generally are not. Almost all kidney cancer is renal cell carcinoma. Another kind of kidney cancer, Wilms' tumor, occurs in children (see Childhood Cancers: Wilms' Tumor).
Symptoms
Blood in the urine is the most common first symptom, but the amount of blood may be so small that it can be detected only under a microscope. On the other hand, the urine may be visibly red. The next most common symptoms are pain in the flank (the area between the ribs and hip), fever, and weight loss. Infrequently, a kidney cancer is first detected when a doctor feels an enlargement or lump in the abdomen.
The red blood cell count may become abnormally high (polycythemia) because high levels of the hormone erythropoietin (which is produced by the diseased kidney or by the tumor itself) stimulate the bone marrow to increase the production of red blood cells. Symptoms of a high red blood cell count may be absent or may include headache, fatigue, dizziness, and visual disturbances. Conversely, kidney cancer may lead to a drop in the red blood cell count (anemia) because of slow bleeding into the urine. Anemia may cause easy fatigability or dizziness. Some people develop high levels of calcium in the blood (hypercalcemia), which may cause weakness, fatigue, slowed reaction times, and constipation.
Diagnosis
Today, most kidney cancers are discovered by chance when an imaging test such as computed tomography (CT) or ultrasonography is done to evaluate another problem, such as high blood pressure. If doctors suspect kidney cancer based on a person's symptoms, they use CT or magnetic resonance imaging (MRI) to confirm the diagnosis. Ultrasonography or intravenous urography may also be used initially, but doctors must use CT to verify the diagnosis. If cancer is diagnosed, other imaging tests (for example, chest x-ray, bone scan, or CT of the head, chest, or both) may be done to determine whether and where the cancer has spread. However, sometimes cancer that has recently spread cannot be detected.
Prognosis
Many factors affect prognosis, but the 5-year survival rate for people with cancer confined to the kidney is 85% or better. If the cancer has spread into the renal vein or the vena cava but has not spread to distant sites, the 5-year survival rate is 35 to 60%. When cancer has spread to distant sites, the 5-year survival rate is no higher than 10%. In some instances, the goal is to focus on pain relief and other means to improve the person's comfort (see Death and Dying: Symptoms During a Fatal Illness). As with all terminal illnesses, planning for end-of-life issues, including creating advance directives, is essential (see Death and Dying: Legal and Ethical Concerns and Legal and Ethical Issues: Advance Directives).
Treatment
When the cancer has not spread (metastasized) beyond the kidney, surgically removing the affected kidney provides a reasonable chance of cure. Alternatively, surgeons may remove only the tumor with a rim of adjacent normal tissue, which spares the remainder of the kidney.
If the cancer has spread into adjacent sites such as the renal vein or even the large vein that carries blood to the heart (vena cava) but has not spread to distant sites, surgery may still provide a chance for cure. However, kidney cancer has a tendency to spread early, especially to the lungs, sometimes before symptoms develop. Because kidney cancer that has spread to distant sites may escape early diagnosis, metastasis sometimes becomes apparent only after doctors have surgically removed all of the kidney cancer that could be found.
Treating the cancer by enhancing the immune system's ability to destroy it causes some cancers to shrink and may prolong survival (see Prevention and Treatment of Cancer: Immunotherapy). One such treatment, interleukin-2, is used for kidney cancer. Various combinations of interleukin-2, interferon, and other biologic agents and even vaccines developed from cells removed from the kidney cancer are being investigated. These treatments may be helpful for metastatic cancer, although the benefit is usually small. For people with metastatic cancer, recently developed treatments include the drugs sunitinib, sorafenib, and temsirolimus. These drugs alter molecular pathways that affect the tumor and are thus called targeted therapies. Rarely (in less than 1% of people), removing the affected kidney causes tumors elsewhere in the body to shrink. However, the slim possibility that tumor shrinkage will occur is not considered sufficient reason to remove a cancerous kidney when the cancer has already spread, unless removal is part of an overall plan that includes other systemic therapies.
Last full review/revision December 2007 by David A. Swanson, MD
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