Kidney cancer is a cancer that starts in the kidneys. To understand more about kidney cancer, it helps to know about the normal structure and function of the kidneys.

About the kidneys

The kidneys are a pair of bean-shaped organs, each about the size of a fist and weighing about 4 to 5 ounces. They are fixed to the upper back wall of the abdominal cavity. One kidney is just to the left and the other just to the right of the spine. Both are protected by the lower ribcage.

The kidneys' main job is to filter blood and rid your body of excess water, salt, and waste products. The filtered waste products are concentrated into urine. Urine leaves the kidneys through long slender tubes called ureters that connect to the bladder. Urine flows down the ureters into the bladder, where it is stored until you urinate.

The kidneys also help make sure the body has enough red blood cells. It does this by making a hormone called erythropoietin, which tells the bone marrow to make more red blood cells.

Although our kidneys are important, we actually need less than one complete kidney to function. Tens of thousands of people in the United States are living normal healthy lives with just one kidney. Some people may not have any working kidneys at all, and survive with the help of a medical procedure called dialysis. Dialysis uses a specially designed machine that acts like a real kidney to filter the blood.

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. It accounts for about 9 out of 10 kidney cancers.

Although RCC usually grows as a single mass within the kidney, sometimes tumors are found in more than one part of the kidney or even in both kidneys at the same time. Some renal cell carcinomas are noticed only after they have become quite large, but most are found before they metastasize (spread) to distant organs in the body. Often they are found on CT scans or ultrasounds being done for concerns other than kidney cancer. Like most cancers, RCC is hard to treat once it has metastasized.

There are several subtypes of RCC, based mainly on how the cancer cells look under a microscope:

Clear cell renal cell carcinoma

This is the most common form of renal cell carcinoma. About 8 out of 10 people with renal cell carcinoma have this kind of cancer. When seen under a microscope, the cells that make up clear cell RCC appear very pale or clear.

Papillary renal cell carcinoma

This is the second most common subtype -- about 10% to 15% of people have this kind. These cancers form little finger-like projections (called papillae) in some, if not most, of the tumor. Some doctors call these cancers chromophilic because the cells take in certain dyes used so the tissue can be seen under the microscope, and look pink.

Chromophobe renal cell carcinoma

This subtype accounts for about 5% 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.

Collecting duct renal cell carcinoma

This subtype is very rare. The major feature is that the cancer cells can form irregular tubes.

Unclassified renal cell carcinoma

In rare cases, 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 cancerous kidney tumors

Less common cancers of the kidney include transitional cell carcinomas, Wilms tumors, and renal sarcomas.

Transitional cell carcinoma

About 5% to 10% of cancers in the kidney are transitional cell carcinomas, also known as urothelial carcinomas. Transitional cell carcinomas begin in the renal pelvis (where the kidney meets the ureter). Under the microscope, the cells look like bladder cancer cells. Studies have shown that, like bladder cancer, these cancers are often linked to cigarette smoking and workplace exposures to certain cancer-causing chemicals.

People with transitional cell carcinoma often have the same signs and symptoms as patients 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 involved surgeries. Chemotherapy is sometimes given after surgery, depending on how much cancer is found. 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 transitional cell carcinomas of the kidney are curable if they are found at an early stage. The chances for cure drop dramatically if the tumor has grown into the ureter wall or main part of the kidney or if it has a more aggressive (high grade) appearance when viewed 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 extremely important because transitional cell carcinoma can come back in the bladder, as well as other places in the body.

Wilms tumor

About 5% of all kidney cancers are Wilms tumors. This type of cancer is almost always found in children and is extremely rare among adults. If you want to learn more about this type of cancer, call 1-800-ACS-2345 and ask for our document, Wilms Tumor.

Renal sarcoma

Renal sarcomas are a rare type of kidney cancer (less than 1% of all kidney tumors) that begin in the kidney's connective tissue. Renal sarcomas are discussed in more detail in our document, Sarcoma -- Adult Soft Tissue Cancer.

Benign (non-cancerous) kidney tumors

Some types of kidney tumors are benign (non-cancerous).This means they do not usually spread (metastasize) to other parts of the body, although they can still grow and cause problems. Benign kidney tumors include renal cell adenomas, renal oncocytomas, and angiomyolipomas.

Renal adenoma

Renal adenomas are the most common form of benign kidney tumor. They are small, slow-growing tumors that often show up on imaging tests (such as CT scans) when the doctor is looking for something else. They look a lot like low-grade renal cell carcinomas under a microscope. In rare cases, tumors first thought to be renal adenomas may turn out to be small renal cell carcinomas. Because they are hard to tell apart, suspected adenomas are often treated like renal cell cancers.

Oncocytoma

Oncocytomas are a type of benign kidney tumor that can sometimes grow quite large. As with renal adenomas, it can sometimes be hard to tell them apart from kidney cancers. Because oncocytomas do not normally spread to other organs, removing the kidney can often produce a cure.

Angiomyolipoma

Angiomyolipomas are another rare benign kidney tumor. They often develop in people with tuberous sclerosis (a genetic condition that also affects the heart, eyes, 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 but they may need to be treated if they cause problems (such as bleeding).

The rest of this document focuses on renal cell carcinoma and not transitional cell carcinomas, Wilms tumors, renal sarcomas, or other less common types of kidney tumors.

Last Medical Review: 02/18/2009
Last Revised: 05/14/2009