What is kidney cancer?
Kidney cancer is a cancer that starts in the kidneys. To understand more about kidney cancer, it helps to know about the kidneys and what they do.
About the kidneys
The kidneys are a pair of bean-shaped organs, each about the size of a fist. They are attached to the upper back wall of the abdomen. One kidney is just to the left and the other just to the right of the backbone. The lower rib cage protects the kidneys.
Small glands called adrenal glands sit above each of the kidneys. Each kidney and adrenal gland is surrounded by fat and a thin, fibrous layer known as Gerota’s fascia.
The kidneys’ main job is to filter the blood coming in from the renal arteries to remove excess water, salt, and waste products. These substances become urine. Urine leaves the kidneys through long slender tubes called ureters, which connect to the bladder. The place where the ureter meets the kidney is called the renal pelvis. The urine is then stored in the bladder until you urinate (pee).
The kidneys also have other jobs:
Our kidneys are important, but we actually need less than one complete kidney to function. Many people in the United States are living normal, healthy lives with just one kidney.
Some people do not have any working kidneys at all, and survive with the help of a medical procedure called dialysis. The most common form of dialysis uses a specially designed machine that filters blood much like a real kidney would.
Renal cell carcinoma
Renal cell carcinoma (RCC), also known as renal cell cancer or renal cell adenocarcinoma, is by far the most common type of kidney cancer. About 9 out of 10 kidney cancers are renal cell carcinomas.
Although RCC usually grows as a single tumor within a kidney, sometimes there are 2 or more tumors in one kidney or even tumors in both kidneys at the same time.
There are several subtypes of RCC, based mainly on how the cancer cells look under a microscope. Knowing the subtype of RCC can be a factor in deciding treatment and can also help your doctor determine if your cancer might be due to an inherited genetic syndrome.
Clear cell renal cell carcinoma
This is the most common form of renal cell carcinoma. About 7 out of 10 people with RCC have this kind of cancer. When seen under a microscope, the cells that make up clear cell RCC look very pale or clear.
Papillary renal cell carcinoma
This is the second most common subtype – about 1 in 10 RCCs are of this type. These cancers form little finger-like projections (called papillae) in some, if not most, of the tumor. Some doctors call these cancers chromophilicbecause the cells take in certain dyes and look pink under the microscope.
Chromophobe renal cell carcinoma
This subtype accounts for about 5% (5 cases in 100) of RCCs. The cells of these cancers are also pale, like the clear cells, but are much larger and have certain other features that can be recognized.
Rare types of renal cell carcinoma
These subtypes are very rare, each making up less than 1% of RCCs:
Unclassified renal cell carcinoma
Rarely, renal cell cancers are labeled as unclassified because the way they look doesn’t fit into any of the other categories or because there is more than one type of cell present.
Other types of kidney cancers
Other types of kidney cancers include transitional cell carcinomas, Wilms tumors, and renal sarcomas.
Transitional cell carcinoma
Of every 100 cancers in the kidney, about 5 to 10 are transitional cell carcinomas (TCCs), also known as urothelial carcinomas.
Transitional cell carcinomas don’t start in the kidney itself, but in the lining of the renal pelvis (where the urine goes before it enters the ureter). This lining is made up of cells called transitional cells that look like the cells that line the ureters and bladder. Cancers that develop from these cells look like other urothelial carcinomas, such as bladder cancer, under the microscope. Like bladder cancer, these cancers are often linked to cigarette smoking and being exposed to certain cancer-causing chemicals in the workplace.
People with TCC often have the same signs and symptoms as people with renal cell cancer − blood in the urine and, sometimes, back pain.
These cancers are usually treated by surgically removing the whole kidney and the ureter, as well as the portion of the bladder where the ureter attaches. Smaller, less aggressive cancers can sometimes be treated with less surgery. Chemotherapy (chemo) is sometimes given before or after surgery, depending on how much cancer is found. The chemo given is the same as that used for bladder cancer. It’s important to talk with your doctor to be aware of your options and the benefits and risks of each treatment.
About 9 out of 10 TCCs of the kidney are cured if they are found at an early stage. The chances for cure are lower if the tumor has grown into the ureter wall or main part of the kidney or if it looks more aggressive (high grade) when seen under a microscope.
After treatment, follow-up visits to your doctor for monitoring with cystoscopy (looking into the bladder with a lighted tube) and imaging tests are very important because TCC can come back in the bladder, as well as other places in the body.
For more information about transitional cell carcinoma, see our document Bladder Cancer.
Wilms tumor (nephroblastoma)
Wilms tumors almost always occur in children. This type of cancer is very rare among adults. To learn more about this type of cancer, see our document Wilms Tumor.
Renal sarcomas are a rare type of kidney cancer that begin in the blood vessels or connective tissue of the kidney. They make up less than 1% of all kidney cancers.
Sarcomas are discussed in more detail in our document Sarcoma- Adult Soft Tissue Cancer.
Benign (non-cancerous) kidney tumors
Some kidney tumors are benign (non-cancerous). This means they do not metastasize (spread) to other parts of the body, although they can still grow and cause problems.
Benign kidney tumors can be treated by removing or destroying them, using many of the same treatments that are also used for kidney cancers, such as surgery, radiofrequency ablation, and arterial embolization. The choice of treatment depends on many factors, such as the size of the tumor and if it is causing any symptoms, the number of tumors, whether tumors are in both kidneys, and the person’s general health.
Renal adenomas are the most common benign kidney tumors. They are small, slow-growing tumors that are often found on imaging tests (such as CT scans) when the doctor is looking for something else. Seen with a microscope, they look a lot like low-grade renal cell carcinomas.
In rare cases, tumors first thought to be renal adenomas turn out to be small renal cell carcinomas. Because they are hard to tell apart, suspected adenomas are often treated like renal cell cancers.
Oncocytomas are benign kidney tumors that can sometimes grow quite large. As with renal adenomas, it can sometimes be hard to tell them apart from kidney cancers. Oncocytomas do not normally spread to other organs, so surgery often cures them.
Angiomyolipomas are rare. They often develop in people with tuberous sclerosis, a genetic condition that also affects the heart, eyes, brain, lungs, and skin. These tumors are made up of different types of connective tissues (blood vessels, smooth muscles, and fat). If they aren’t causing any symptoms, they can often just be watched closely. If they start causing problems (like pain or bleeding), they may need to be treated.
The rest of this document focuses on renal cell carcinoma and not on less common types of kidney tumors.