The kidneys are two bean-shaped organs located deep inside the torso to the left and right of the backbone, in the area around the waist. Each kidney is about the size of an open hand and works independently to filter impurities and excess salts such as potassium and sodium from the blood. The kidneys process these wastes to generate urine. Urine is concentrated in a central funnel-like reservoir within the kidneys called the renal pelvis, also known as the collecting system. It is then passed down long, slender tubes called ureters, which connect the kidneys to the bladder.
Primary kidney cancer, also called renal cell cancer, is a malignant tumor that originates in the kidney. There are two main types of primary kidney tumors — renal cortical tumors (about 90 percent of tumors) and transitional cell (also called urothelial) tumors. Each of these tumor types arises from different parts of the kidney and requires different approaches for treatment.
Kidney cancer affects more than 55,000 people in the United States each year. It occurs more often in men than in women.
Types of Kidney Cancer
Each kidney contains more than a million microscopic blood-processing filtering units called nephrons. Each nephron is associated with a microscopic renal tubule, which joins several other tubules from other nephrons to form collecting ducts. These ducts deposit the urine in the renal pelvis. When cancer arises in the main part of the kidney that contains the renal tubules, it is called a renal cortical tumor. Cancer that arises in the renal pelvis is called a transitional cell (urothelial) tumor.
Renal Cortical Tumors
Renal cortical tumors are a diverse group of tumor types that can exhibit very different clinical behaviors, meaning that their risk of spreading to other areas of the body varies. These tumors can be either benign (noncancerous) or malignant (cancerous). Renal cortical tumors are categorized into the following types:
- Conventional, or clear cell, which accounts for 60 to 65 percent of cases.
- Papillary, also known as chromophil, which makes up 10 to 15 percent of cases.
Papillary carcinomas can develop as individual or multiple tumors, appearing either in the same kidney or in both kidneys. There are two types of papillary cancers, type 1 and type 2. Type 1 are more common and usually grow slowly. Type 2 papillary tumors represent more than one category of disease but, as a group, are much more aggressive and may follow an unpredictable growth pattern.
Papillary carcinomas have been associated with genetically inherited syndromes, including hereditary papillary renal cell carcinoma (HPRCC) and hereditary leiomyomatosis and renal cell carcinoma (HLRCC). HLRCC is a relatively rare, inherited form of kidney cancer that is difficult to diagnose before surgery in patients without a known family history of the disease. Genetic testing is available for individuals suspected of having the syndrome.
- Chromophobe, which accounts for 5 to 10 percent of kidney tumors. These are considered a less aggressive form of primary kidney cancer. Chromophobe tumors may reach a very large size before there is any risk of spreading outside the kidney.
- Oncocytoma, which makes up 5 to 10 percent. Oncocytomas have almost no risk of spreading or causing death.
- Collecting duct, which makes up less than 1 percent. This is a very rare and aggressive type of tumor that is more common in younger adults and doesn't respond to conventional therapies for renal cortical tumors.
- Unclassified, which makes up 3 to 5 percent. These rare tumors look different under the microscope than other kidney cancer subtypes and are usually very aggressive.
Transitional Cell (Urothelial) Tumors
Transitional cell tumors of the kidneys and ureters are similar to bladder tumors. The type of cells that line the inside of the bladder also line the inside of the ureters and the renal pelvis. Cancers that arise from these cells behave similarly, whether they grow in the bladder or in the collecting system (renal pelvis and ureter). Doctors manage such lesions differently than renal cortical tumors, depending on several factors including tumor grade, location, and size.
Low-grade transitional cell (urothelial) tumors that can be reached with a thin fiber-optic scope can sometimes be treated successfully using laser energy or electrocautery (using an electrically heated needle to destroy tumor tissue). High-grade tumors represent a much greater risk, and more aggressive forms of treatment are typically recommended. Such treatment may include removal of the entire kidney and attached ureter leading down to the bladder.
With both low- and high-grade tumors, the initial diagnosis depends on both the results of imaging studies and microscopic analysis of a tissue sample. The means by which the tumor sample is obtained depends on the clinical situation. For more information about transitional cell tumors, visit the bladder cancer section on our Web site.
Not all masses found in the kidneys are renal cancers. Other types of masses include benign conditions such asoncocytomas, angiomyolipomas (AML), and renal cysts. Both renal cysts and AML lesions have identifiable characteristics that can be seen on imaging studies and usually do not require treatment.
Certain types of cancers from other parts of the body, such as breast, lung, and skin cancers, can spread to the kidneys. Lymphoma can also be found in the kidney. How these diseases are evaluated and treated depends on what other findings are present, including the extent of the original cancer.
Kidney cancer rarely strikes children and young adults; the exceptions are a pediatric kidney cancer called Wilms' tumor and some forms of hereditary kidney cancer syndromes, such as von Hippel-Lindau (VHL) disease. Memorial Sloan-Kettering is a recognized Clinical Care Center for families with VHL disease. Patients with hereditary forms of kidney cancer often require specialized approaches to diagnosis and management, including genetic counseling and coordinated evaluation with other medical specialties. Our team of experts is very familiar with these special needs and has developed programs dedicated to the care of patients with hereditary cancer syndromes.
Kidney cancer usually shows no symptoms in the early stages. Generally, it is not suspected until symptoms appear; by that point, the tumor may have grown fairly large. As the cancer progresses, symptoms may include some of the following:
- blood in the urine
- lower back pain that cannot be accounted for by something else (such as an injury)
- a mass or lump in the abdomen
- unexplained weight loss, which may be rapid
- fever that is not due to a cold or flu
- swelling of the ankles and legs (due to an impaired ability to rid the body of liquid waste)
Some of these symptoms may be due to other causes, such as an infection. Your doctor can determine what is causing them and how they should be treated.
Studies have shown that certain lifestyle factors can increase the risk of developing kidney tumors. Smoking, having high blood pressure, eating a high-fat diet, and being overweight all may contribute to an increased risk of kidney cancer. Although we do not know all the causes of kidney cancer, the following factors can also increase the risk of developing this disease:
- long-term dialysis, a process in which a machine filters the blood of a person without functioning kidneys
- exposure to asbestos, such as occupational exposure
- exposure to cadmium, a metal that can increase the cancer-causing effect of smoking
If you are exposed to asbestos or cadmium at work, be sure to follow occupational safety practices that limit your exposure.
Hereditary Kidney Cancer
A family history of kidney cancer and/or certain hereditary diseases also increase the risk of kidney cancer:
- von Hippel-Lindau (VHL) disease, a syndrome caused by a genetic mutation that leads to multiple tumors in the kidney, often at an early age, and may also include brain and eye hemangiomas, pancreas cysts, and adrenal tumors
- Birt-Hogg-Dubé syndrome (BHD), an inherited skin disease affecting the hair follicles and associated with kidney tumors and air pockets in the lungs
- hereditary papillary renal carcinoma (HPRC), an inherited form of kidney cancer characterized by papillary renal cancer in younger patients, which are typically multiple and bilateral (in both kidneys)
- hereditary leiomyomatosis and renal cell carcinoma (HLRCC), an extremely rare inherited genetic mutation in which affected individuals may have skin bumps, women often have large fibroids of the uterus that cause severe menstrual bleeding, and men and women are at risk for aggressive forms of kidney cancer
- tuberous sclerosis, a genetic disorder characterized by severe skin bumps, seizures, mental retardation, and cysts in the kidneys, liver, and pancreas
- Other inherited conditions are also known to be associated with kidney and adrenal tumors. Physicians and researchers at Memorial Sloan-Kettering are investigating several of them.
Genetic testing is required to determine whether hereditary factors might increase your risk for kidney cancer. Our kidney cancer experts can help determine whether genetic testing studies are appropriate in your case, and refer you to our Clinical Genetics Service for genetic counseling.
Because kidney cancer is less common in the United States than many other cancers, there are no widely used screening programs, and regular examinations to detect it are not recommended. However, if you have been on long-term kidney dialysis or have a history of VHL or other forms of hereditary kidney cancer, you may benefit from periodic evaluation to check for the development of kidney tumors.
If you have a hereditary form of kidney cancer, we offer screening studies to evaluate your family members who may also be at risk. Identifying high risk for kidney cancer can make early, curative intervention possible.