Cancer of the kidney is diagnosed in approximately 30,000 people in the United States and 3,900 people in Canada each year. Men have twice the risk of women, and smokers have twice the risk of nonsmokers. Excess weight also increases the risk of developing kidney cancer. Some studies show a link between occupational exposure to asbestos or cadmium and kidney cancer.
The kidneys, two bean-shaped organs on either side of the spine, filter the blood and rid the body of waste through urine. In adults, most kidney cancers develop in the tissues that filter blood and produce urine. This type of cancer is called renal cell cancer and accounts for 85 percent of all cancers of the kidney. Cancer of the renal pelvis, a cavity in the center of each kidney, is similar to certain cancers of the bladder and is called transitional cell carcinoma. Wilms' tumor, the most common kidney cancer in children, results when developing kidney cells fail to mature and instead divide uncontrollably, forming a mass of immature cells.
The most common symptom of kidney cancer is blood in the urine. A lump or a mass that can be felt in the kidney area may also be an indication of kidney cancer. As kidney cancer grows, it may invade organs near the kidney, such as the liver, colon, or pancreas. The five-year survival rate in the United States for adult kidney cancer is 58 percent but rises to nearly 88 percent if the tumor is detected before it spreads.
The kidneys filter the blood and rid the body of wastes. Approximately one million nephrons (right) compose each bean-shaped kidney (left). The filtration unit of the nephron, called the glomerulus, regulates the concentration within the body of important substances such as potassium, calcium, and hydrogen, and removes substances not produced by the body such as drugs and food additives. Cancers that originate in the filtration tissues of the kidney, called renal cell cancer, account for 85 percent of all cancers of the kidney. A small percentage of cancers originate in the renal pelvis, a cavity in the center of each kidney.