What Is Kidney Cancer?

Kidney cancer happens when cells in one or both kidneys start to grow out of control. Eventually, the cells become a mass called a tumor. As the cancer progresses, it can spread to other parts of the body.

This article discusses kidney cancer, its types, symptoms, and causes. It also looks at how kidney cancer is diagnosed and treated.

Kidney Anatomy and Function

The kidneys are two bean-shaped organs. Each is about the size of a small fist. They are located behind the abdominal organs with one on each side of the spine.

Some people have only one kidney. This can happen as a result of either a birth defect or illness. It is possible to live well with only one kidney, as long as the kidney is functional.

Your kidneys remove excess minerals, salt, and water from the blood in the form of urine. Each day, the kidneys filter roughly 50 gallons of blood and produce about two quarts of urine. The urine is passed down tubes called ureters into the bladder, where it’s kept until you urinate.

The filtering units in your kidneys are called nephrons. There are over one million of these units in each kidney. Inside a nephron, a structure called a glomerulus acts as a filter. Another structure called a tubule removes waste products and returns important substances to your bloodstream.

Types of Kidney Cancer

There are several types of kidney cancer, including:

• Renal cell carcinoma: This is by far the most common form of kidney cancer. It accounts for about 85% of cases.
• Transitional cell carcinoma: Around 5% to 10% of kidney cancers are transitional cell carcinomas. These arise from the same type of cells involved in bladder cancer. Transitional cell carcinoma is treated more like bladder cancer than renal cell carcinoma.
• Wilm’s tumor: Wilm’s tumor is a cancer that usually develops during childhood. Among childhood cancers, it is relatively common.
• Renal sarcoma: Sarcoma of the kidney is a rare tumor. It often starts in the connective tissue of the kidney.

Because renal cell carcinoma is the most common type, most of the information below pertains to this type.

Kidney Cancer Symptoms 

Kidney cancer symptoms do not usually appear until the disease has progressed. When symptoms occur, they may include:

• Blood in the urine, either seen after urination or microscopically
• Fatigue
• A mass on the side or lower back (flank mass)
• Pain on the side or lower back (flank region)
• Fever
• High blood pressure
• Unintentional weight loss

What Causes Kidney Cancer?

The exact causes of kidney cancer are not yet known. Researchers have identified several risk factors for kidney cancer, however. Some of these include:

• Age: The risk of kidney cancer increases with age. Most renal cell carcinomas occur in people over the age of 40. Wilm’s tumor is more common in children.
• Sex: Kidney cancer is more common in males than in females.
• Race: Kidney cancer is slightly more common in Black people and Indigenous Americans.
• Smoking: People who smoke have an increased risk of kidney cancer.
• Occupation: Workplace exposures to certain substances such as asbestos and benzene increase risk.
• Obesity
• Family history: A family history of kidney cancer or certain genetic syndromes increase risk.
• Medications: Use of certain medication, such as calcium channel blockers, can increase kidney cancer risk.

How Kidney Cancer Is Diagnosed

Historically, the most common presenting symptoms of kidney cancer were:

• Flank pain (pain on the side and lower back)
• An abdominal mass
• Blood in the urine
• Anemia

Today, kidney cancer is often discovered during imaging tests for another condition, such as an X-ray, CT scan, or MRI.

When a healthcare provider suspects kidney cancer, a CT scan can be used to look at the kidneys. This test combines multiple X-ray images into a 3-dimensional picture of internal body structures. It may involve an intravenous contrast medium, a dye that makes internal structures appear better in the images. It can also help to distinguish cancer from non-cancerous cysts.

A CT scan can be used for both the detection and staging of kidney cancer. Staging is the process of determining how large the tumor is and if it has spread.

Some people are unable to have a CT. This could be because of allergies to the contrast materials or poor kidney function. People who can’t have a CT scan may receive an MRI instead. An MRI uses magnetic imaging rather than X-rays. MRI is also helpful if a tumor is thought to have spread into the veins near the kidneys.

A biopsy lets pathologists look for cancer cells under a microscope. This can be very helpful in guiding treatment with targeted therapies. Samples are usually obtained during surgery to treat cancer rather than during the diagnostic process.

Staging

If cancer is found, more tests may need to be done to determine if it has spread to nearby tissues or organs.

Kidney cancer is staged by measuring the size of the tumor within the kidney’s structures. Your healthcare provider will also look for evidence of spread to nearby tissues or distant regions of the body.

Treatment Options

Kidney cancer is somewhat unique. This is because surgery may be done even with advanced tumors. Targeted therapies and immunotherapy drugs may also be used. Chemotherapy and radiation therapy plays a lesser role than with some other cancers.

Treatments for kidney cancer depend upon the stage of the disease and many other factors. Your general health and the location of the cancer in your kidney, for example, will help guide treatment decisions.

Surgery is the treatment of choice for most kidney cancers. For some patients, though, it can be difficult. Very elderly people or those with multiple serious medical conditions may not be able to tolerate surgery. In these cases, treatments like cryosurgery (freezing), or radiofrequency ablation (burning), may be options.

Kidney Cancer Doctor Discussion Guide

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Several targeted therapy drugs have been approved for use in some people with advanced kidney cancer. These drugs block and prevent the growth and spread of malignant cells. They do this by directly interfering with a pathway involved in cancer growth. They may also prevent the growth of blood vessels needed to supply the tumor with nutrients.

The side effects of these drugs are different from those of chemotherapy. These drugs are often also better tolerated.

Immunotherapy, also known as biologic therapy, works by stimulating the body’s own immune system to fight off cancer cells. A few different categories of these drugs are effective for kidney cancer.

Radiation is not commonly used as a treatment for kidney cancer. It may be used palliatively to relieve the discomfort that can happen when cancer spreads. Chemotherapy has only a limited effect against some kidney cancers, though it’s more effective against transitional cell carcinoma and Wilm’s tumor.

Summary

There are several types of kidney cancer. The most common is renal cell carcinoma. Symptoms of kidney cancer can include blood in the urine, pain in the side or lower back, and unintentional weight loss. Kidney cancer is sometimes found during imaging scans for other conditions.

Kidney cancer is often treated with surgery, even in the later stages. It may also be treated with targeted therapy drugs.

A Word From Verywell

It’s important to be aware of kidney cancer's potential symptoms and risk factors. This can help ensure that if you do develop kidney cancer, it’s caught in the early stages. There are many treatment options available for kidney cancer.

That said, an ounce of prevention beats a pound of cure. There are many steps you can take to reduce your risk. Smoking is a strong risk factor for kidney cancer. If you smoke, quit. If you don’t, don’t start. Risk does decrease when you quit, so it’s never too late. There are also many reasons to quit smoking after a cancer diagnosis.

Take the time to learn about any chemicals or other substances you are exposed to at work. If you do contact these chemicals in the workplace, make sure to follow the recommended precautions. Finally, eating a healthy diet and maintaining a healthy weight is important. Obesity is a risk factor for many cancers, not just kidney cancer.