Kidney cancer, also known as renal carcinoma, starts in the cells of one or both kidneys, and the cancer type depends on where in the organ the disease starts.
The kidneys have a number of important tasks: They're responsible for cleaning and processing blood, removing the excess water and waste, then discarding that waste in the form of urine. And via the hormone-secreting adrenal gland attached to the top of each one, they have a number of regulatory functions, including helping to maintain metabolism, blood pressure, and red blood-cell production. Cancer in these organs can interfere with any or all of these functions.
Types of Kidney Cancer
Kidney cancer can have many forms but, according to the American Cancer Society, more than 90 percent of all cases in adults are renal cell carcinomas. Renal cell carcinomas start in the lining of the kidney filtration tubes, which the kidney uses to filter waste and toxins from the blood.
In children, the most common type of kidney cancer is one called Wilms tumor.
Kidney Cancer Risk Factors
While researchers have not yet uncovered the direct cause of kidney cancer, some people are more at risk than others. Risk increases with age, with the majority of kidney-cancer cases occurring in people over 45 and the highest rate in those between the ages of 55 and 84. Men are twice as likely to develop it than women, and African American men have a slightly higher risk than Caucasian men.
Certain behaviors also increase risk of kidney disease. Studies have consistently shown that smokers have a higher risk than nonsmokers, and that risk goes up the longer someone smokes. Obesity and hypertension (high blood pressure) also increase risk; about 40 percent of renal cell cancers in the United States are related to excess body weight.
Kidney cancer incidence is increasing by approximately 2 percent per year, but no one knows why. Some research, from the Kidney Cancer Research Network of Canada, suggests this increase may be a result of the radiation exposure that comes from the increased use of abdominal imaging techniques such as CT (computed tomography) scans.
Kidney Cancer Symptoms
Signs and symptoms of kidney cancer include:
Blood in the urine (hematuria) - When blood is mixed with urine, the resulting fluid may look dark red or brownish red
Abdominal pain or consistent pain in the side (flank pain)
A mass or lump in the abdomen or flank
Fever and lethargy or a feeling of exhaustion
Kidney Cancer Diagnosis
Kidney cancer can be detected through a physical exam and a number of other diagnostic tests. Often, physicians will start by recommending active surveillance. This is normally recommended for tumors smaller than 3 cm in size, because they may or may not be cancerous. A urologist or other specialist monitors the tumor carefully, watching its size and periodically ordering urine and blood tests to screen for disease signifiers such as red blood cells in urine or high levels of creatinine. The tumor is removed if it grows quickly or exceeds 4 cm in size.
If blood or urine tests indicate reason for concern, imaging techniques can confirm or negate the presence of cancer. These include:
CT scans: These help a doctor visualize your organs and their surrounding tissues in order to determine whether a tumor is present. The scans (with or without contrast dye) can also determine the cancer's aggressiveness by examining lymph nodes and nearby tissue for presence of disease.
Magnetic resonance imaging (MRI): This can detect any abnormalities in the urinary tract, lymph nodes, kidneys, or surrounding tissues. In some cases, contrast material may be required to create a more detailed image. Because contrast dye displays clearly on X-rays, using contrast can help make a more accurate diagnosis, or even aid a surgeon in planning the procedure.
If imaging tests detect an anomaly, the physician will recommend a biopsy. The resulting sample will be sent to a pathologist, who will examine it, determine whether the tissue is malignant or benign, and what type of cancer it is.
Treating Kidney Cancer
The first step in treating kidney cancer is staging, which assesses the cancer's size and aggressiveness. To do this, an oncologist or other specialist will gauge how far the cancer has spread. While identification of cancerous cells is important, most doctors believe that the stage of the cancer is the most important factor in predicting prognosis.
There are four stages of kidney cancer (also known as renal carcinoma):
Stage I: when tumor size is smaller than 7 cm, about the size of a baseball, with cancerous cells confined to the kidney
Stage II: when tumor is larger than 7 cm in diameter and has not yet spread to other tissues
Stage III: when the tumor is growing in a major vein or into the adrenal gland, or when the cancer has spread to nearby lymph nodes but not distant lymph nodes or other organs
Stage IV: when the cancer has progressed beyond the kidney and lymph nodes and metastasized in the tissue encasing the kidney, or in the liver, lungs, or other tissues
Treatment depends on a number of factors, including potential side effects, the patient's age, and the size, stage, and invasiveness of the tumor.
1. Jewett M, Finelli A, Soulieres O, et al. Management of Kidney Cancer: Canadian Kidney Cancer Forum Consensus Update 2011. Canadian Urological Association Journal. February 2012;6(1):16-22.
2. Jewett M, Mattar K, Fernandes K, et al. Active Surveillance of Small Renal Masses: Progression Patterns of Early Stage Kidney Cancer. European Urology. July 2011;60(1):39-44.
3. Renal and Adrenam Tumors Biology and Management. Edited by Are Belldegrun, Alastair Ritchie, et al. 2003. Oxford University Press.